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The management of sewage sludge is a recognized and pressing issue. Traditional and innovative sludge minimization processes are applied at full-scale or are at the research stage. However, the processes traditionally applied in wastewater treatment plants (WWTP), at times, have a not fully exploited potential due to a lack of process optimization. Therefore, careful monitoring, coupled with functionality checks and experimental tests, can provide useful indications for maximizing the performance of the treatment units already in place. In this work a full-scale experimental campaign was set up in a recently renewed WWTP, to investigate the potential of aerobic sludge stabilization in reducing the volume of sludge produced and, consequently, the management costs. Operating data were collected and analysed. Two tests were conducted in a stabilization tank, varying the dissolved oxygen (DO) concentration (1 mg/L and > 3 mg/L). The energy consumption was monitored. A model of the volatile suspended solids removal was built, and results were ultimately compared after homogenization. The reduction of volatile suspended solids was 60% and 44%, respectively. The reduction of the quantity of sludge obtained in the two tests was 38% and 29%, respectively. Improved sludge stabilisation rather than sludge reduction was achieved by pushing aerobic stabilisation. The modelled sludge reduction after 2 weeks of treatment would have been 12% and 15% under the tested conditions, respectively. It resulted that, for contact times up to 2 weeks, the DO concentration had not a relevant influence on the sludge stabilization, while consuming more energy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The impact of oxic-settling-anaerobic (OSA) cycle and SRT on sludge yield was studied. • OSA implementation reduced sludge production by 38–48 % at the SRT of 20 d. • OSA implementation at SRT of 60 d showed no significant impact of sludge yield. • Tripling the HRT in the anaerobic tank improved sludge reduction at the SRT of 60 d. • OSA addition and SRT had opposite effects on sludge filterability and settleability. Sewage sludge production represents a critical issue nowadays. The oxic-settling-anaerobic (OSA) system is a promising strategy for reducing sludge production during biological wastewater treatment. However, the distinct effect of OSA process and solid retention time (SRT) on sludge production has not been clarified yet. Therefore, during this study, the impacts of OSA system implementation at different SRT on sludge generation, membrane operation, and contaminant removal were elucidated in two lab-scale membrane bioreactors working at 20 d (MBR 20) and 60 d (MBR 60). After OSA implementation, the MBR-OSA 20 and MBR-OSA 60 were operated at a hydraulic retention time in the sludge holding tank (HRT SHT) of 6–12 h and of 6–24 h, respectively. The estimated observed sludge yield (Y obs) showed a reduction of 38–48 % for the MBR-OSA 20 , but no beneficial effect was observed for MBR-OSA 60 at 6 h of HRT SHT. At the HRT SHT of 24 h, Y obs decreased by 17 % due to hydrolysis and acidogenic biomass fermentation. OSA implementation and long SRT had no negative effects on organic carbon and ammonium removal (96(±3) % and 100 %, respectively) and improved total nitrogen (TN) reduction by 19–41 %. Membrane fouling and sludge filterability were not significantly affected, whereas sludge settleability worsened after the implementation of the OSA cycle. This activity provided additional insights about the distinct impact of the OSA process and SRT on sludge production and characteristics, confirming the OSA process as a valid solution for reducing sludge production under a moderate SRT, but revealing a negligible effect on Y obs under a prolonged SRT and a short HRT SHT. [ABSTRACT FROM AUTHOR]

[Display omitted] Identify sustainable biological sewage sludge (BSS) management represents a current challenge. In this work, pre-thickened BSS taken from a large-scale urban wastewater treatment plant (WWTP) was fed continuously for about 9 months to a semi-industrial scale thermophilic biological fluidized bed reactor (TBFBR) operating in alternate conditions. The BSS treated in TBFBR was strongly reduced (89–92%) and the production was evaluated in 0.0007–0.0023 kg kg CODremoved −1 d−1 and 0.0004–0.0014 kg kg CODremoved −1 d−1 of TS and VS, respectively. The 92% of the P-PO 4 3- and P-org precipitated in inorganic form and accumulated in thermophilic biological sludge (TBS). In basic soils with chelating activity, phosphorus contained in TBS presented a higher bioavailability (84.0 ± 25.3%) with respect to untreated sludge. The analysis of four diverse scenarios highlighted that TBFBR located after pre-thickening could save 73–96% of operating costs with respect to current situation. [ABSTRACT FROM AUTHOR]

• The AET was studied as a novel parameter affecting excess sludge minimization. • Sludge minimization efficiency was statistically dependent on the AET. • Cell lysis and EPS destruction were enhanced by operating at high AET in the ASSR. • AET was better correlated to YOBS reduction than other parameters like ASLR and HRT. • Sludge minimization mechanisms showed a clear dependence on AET. Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields. To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Y obs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10–60 %) with the increase of the AET (7.9–13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Y obs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Y obs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=−0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the effects of different operating conditions on excess sludge minimization in an oxic-settling-anaerobic (OSA) process were evaluated. The experiment involved two systems operating in parallel, one implementing the OSA process and a conventional activated sludge (CAS) system as control, both configured according to a pre-denitrification scheme. Five periods (P1–P5) were studied, during which the OSA was operated under different layouts, which differed from the returned sludge to the anoxic (A) or aerobic (B) mainstream reactors and the hydraulic retention time in the anaerobic reactor of the OSA system (8–12 h). The excess sludge production in the OSA plant was lower in all the investigated configurations, indicating that successful sludge minimization was achieved. Specifically, the sludge production was lowered by approximately 12% (P1), 29% (P2), 40% (P3), 26% (P4) and 41% (P5). Scheme A enabled the establishment of the uncoupling metabolism and the extracellular polymeric substance (EPS) destructuration. In contrast, scheme B enabled the establishment of the maintenance metabolism in addition to the uncoupling metabolisms, whereas cell lysis and EPS destruction were minimized. This allowed for obtaining higher sludge reduction yield (26–40%) without compromising the effluent quality.

In the present paper, a new process, whose acronym is UTN (University of Trento) system, is proposed and tested at full scale for reducing the amount of sludge of the wastewater treatment plant. The UTN system allows sludge reduction in conventional activated sludge (CAS) due to the cell lysis, the sludge decay and, above all, to the selection of slow growing microorganism. In this study, the first full-scale UTN system was tested by retrofitting an existing wastewater treatment plant located in Marmirolo (Lombardia, Italy) having a treatment capacity of 6,000 population equivalent (PE). Performances of the UTN system were evaluated in terms of sludge reduction, together with organic carbon and nutrients removal efficiencies. Results obtained over 10 month of monitoring period, divided in period I (7 months) and period II (3 months), characterized by different operative conditions, have reported a specific sludge production of 0.37 and 0.23 kg TSS per kg of COD removed, respectively; which is 50% and 69% lower than that observed in the reference period when the plant worked under conventional activated sludge process. Furthermore, results revealed that the UTN system allows a high removal of wastewater typical pollutants, without causing negative effects on the effluent quality, always ensuring compliance with the regulatory discharge limits.

Minimizing the biological sewage sludge (BSS) produced by wastewater treatment plants (WWTPs) represents an increasingly difficult challenge. With this goal, tests on a semi-full scale Thermophilic Alternate Membrane Biological Reactor (ThAlMBR) were carried out for 12 months. ThAlMBR was applied both on thickened (TBSS) and digested biological sewage sludge (DBSS) with alternating aeration conditions, and emerged: (i) high COD removal yields (up to 90%), (ii) a low specific sludge production (0.02–0.05 kgVS produced/kgCODremoved), (iii) the possibility of recovery the aqueous carbon residue (permeate) in denitrification processes, replacing purchased external carbon sources. Based on the respirometric tests, an excellent biological treatability of the permeate by the mesophilic biomass was observed and the denitrification kinetics reached with the diluted permeate ((4.0 mgN-NO3−/(gVSS h)) were found comparable to those of methanol (4.4 mgN-NO3−/(gVSS h)). Moreover, thanks to the similar results obtained on TBSS and DBSS, ThAlMBR proved to be compatible with diverse sludge line points, ensuring in both cases an important sludge minimization.

The high energy consumption and excessive waste activated sludge (WAS) production have become the major concerns on the municipal wastewater treatment with conventional biological processes. To tackle these emerging issues, this study demonstrated the feasibility of a novel process integrating an upflow anaerobic fixed-bed reactor (UAFBR) followed by a continuous step-feed reactor for mainstream deammonification towards improved energy efficiency, minimized sludge production and cost-effective ammonium removal. The results showed that 48.8% of the influent chemical oxygen demand (COD) was directly converted to methane gas in UAFBR with minimized sludge production, while 80% of total nitrogen (TN) was removed in the step-feed reactor. Mass balance on the step-feed reactor revealed that the oxic chambers contributed 51.6% of the removed ammonium oxidation to mainly nitrite, while the produced nitrite was immediately removed via anammox with the ammonium supplied by the step-feed in the following anoxic chambers where about 87.1% TN removal occurred. Moreover, it was found that sustainable repression of nitrite oxidizing bacteria (NOB) was achieved without compromising the activity of ammonia oxidizing bacteria (AOB). The anammox bacteria were effectively retained in the anoxic chambers and showed a high specific anammox activity of 0.42 g N/(g VSS·day). These suggest that the step-feed configuration can offer a feasible engineering option towards single-stage mainstream deammonification. It appears that the integrated process developed in this study sheds light on the possible way towards sustainable, energy self-sufficient municipal wastewater reclamation. Unlabelled Image • An integrated process was developed for sustainable wastewater reclamation. • Step-feed configuration was favorable for stable mainstream deammonification. • Effective NOB repression was observed without affecting AOB and anammox activity. • 80% of nitrogen was autotrophically removed via mainstream anammox. • The process offered a feasible engineering solution for stable mainstream anammox. [ABSTRACT FROM AUTHOR]

A lab-scale integrated fixed-film activated sludge (IFAS) reactor was mplemented with the oxic-settling anaerobic (OSA) cycle for reducing sewage sludge production through the addition of an anoxic/anaerobic sludge holding tank (SHT) along the sludge recycle line. The IFAS-OSA system was operated under the different hydraulic retention time (HRT) in the SHT (HRT SHT) of 12 h and 6 h, at an oxidation-reduction potential (ORP) < −91 mV and solid retention time (SRT) between 39 and 126 d. Furthermore, the effect of temperature increase in the SHT (T SHT) from ambient (19.8–25.6 °C) to mesophilic (35 °C) conditions was investigated. The system performances were monitored in terms of sludge minimization and dewaterability efficiencies as well as carbon and nutrients reduction. The observed sludge yield (Y obs) for the IFAS system was 0.37(±0.06) mg VSS/mg COD. After OSA implementation Y obs decreased by 32% and 46–65% at HRT SHT of 12 h and 6 h, respectively, indicating that prolonged exposure to anoxic/anaerobic conditions was not beneficial for sludge reduction. The lowest Y obs of 0.09(±0.05) mg VSS/mg COD (76% lower than that in the IFAS system) was obtained at an HRT SHT of 6 h and when T SHT was set at 35 °C. OSA implementation did not affect COD and NH 4 + oxidation of the IFAS system (90–96% and 99%, respectively) and improved total nitrogen (TN) reduction (31–53%) due to improved denitrification in the SHT. On the contrary, sludge dewaterability worsened following OSA implementation, which was linked to the increased levels of exopolymeric substances in the suspended biomass. [Display omitted] • Integrated fixed-film activated sludge was paired to oxic settiling anaerobic (OSA). • Sludge reduction between 32% and 76% was obtained with the combined system. • Temperature increase to 35 °C in the anoxic holding tank enhanced sludge reduction. • OSA implementation promoted denitrification and enhanced nitrogen removal by 31–53%. • Sludge dewaterability was correlated to exopolymeric substances in suspended phase. [ABSTRACT FROM AUTHOR]

The activated sludge process is the most widely used on a global scale for the biological treatment of both domestic and industrial effluents. One problem associated with the process, however, is the high volume of sludge produced. Excess sludge treatment and disposal account for up to 60% of the total operating costs of urban wastewater treatment plants due to the stringent environmental regulations on excess sludge disposal. These strict requirements have encouraged a growing interest over the last few years in reducing sludge volumes produced at biological treatment plants and a number of physical, chemical, and mechanical methods have been accordingly developed for this purpose. The proposed methods are disadvantaged due to their rather high investment and operation costs. An alternative technology that avoids many of these limitations is the worm reactor. In this study, the characteristics of this technology are investigated while the related literature is reviewed to derive the optimal conditions for the operation of this process in different situations.

Sludge reduction based on regulating substrate allocation between catabolism and anabolism as a strategy is proposed to reduce energy and chemicals consumption during wastewater treatment. The results indicated that a sludge reduction of 14.8% and excellent nutrient removal were simultaneously achieved in the low dissolved oxygen (LDO) activated sludge system with a hydraulic retention time of 24 h at 25 °C. Denitrifiers comprised nearly 1/4 of all microorganisms in the system. These denitrifiers converted NO x − to N 2 obtaining a lower biomass yield. The oxidoreductase activity proteins in the LDO sample was more than twice that of the normal DO sample, indicating that catabolism was stimulated by NO x − when replacing O 2 as electron acceptor. Less substrate was used for cell synthesis in the LDO system. Stable sludge reduction without extra energy and chemicals inputs was achieved by regulating the substrate allocation by inducing the bacteria to utilize NO x − instead of O 2 . [ABSTRACT FROM AUTHOR]

Applying ozone to the return flow in an activated sludge (AS) process is a way for reducing the residual solids production. To be able to extend the activated sludge models to the ozone-AS process, adequate prediction of the tri-atoms effects on the particulate COD fractions is needed. In this study, the biomass inactivation, COD mineralization, and solids dissolution were quantified in batch tests and dose-response models were developed as a function of the reacted ozone doses (ROD). Three kinds of model-sludge were used. S1 was a lab-cultivated synthetic sludge with two components (heterotrophs X H and X P ). S2 was a digestate of S1 almost made by the endogenous residues, X P . S3 was from a municipal activated sludge plant. The specific ozone uptake rate (SO 3 UR, mgO 3 /gCOD.h) was determined as a tool for characterizing the reactivity of the sludges. SO 3 UR increased with the X H fraction and decreased with more X P . Biomass inactivation was exponential (e −β.ROD ) as a function of the ROD doses. The percentage of solids reduction was predictable through a linear model (C Miner + Y sol ROD), with a fixed part due to mineralization (C Miner ) and a variable part from the solubilization process. The parameters of the models, i.e. the inactivation and the dissolution yields (β, 0.008–0.029 (mgO 3 /mgCOD ini ) −1 vs Y sol , 0.5–2.8 mg COD sol /mgO 3 ) varied in magnitude, depending on the intensity of the scavenging reactions and potentially the compactness of the flocs for each sludge. [ABSTRACT FROM AUTHOR]

Elemental sulfur can serve as an economical external sulfur source replacing sulfate as an electron acceptor in sulfidogenic processes for wastewater treatment with sludge minimization. However, the biological sulfur reduction has not yet been considered in wastewater treatment due to the insolubility of sulfur. In this study, a laboratory-scale sulfur-reducing anaerobic fluidized bed (SRAFB) reactor was built to investigate the feasibility of the high-rate sulfur-reducing anaerobic wastewater treatment process. After 273 d of operation, the organics removal and sulfide production rates were determined as 1.71 kg CODc/m 3 -d (CODc: carbonaceous COD) and 2.71 kg S/m 3 -d, respectively, at a high organic loading rate of 2.14 kg CODc/m 3 -d with a hydraulic retention time of only 3 h. Biofilm growth on sulfur particles resulted in high sludge settleability (23 ± 3 mL/g of SVI 30 ) (SVI 30 : sludge volume index in 30 min) and thus high sludge concentration. As expected, a low sludge yield of 0.16 kg VSS/kg CODc (VSS: volatile suspended solids) was also obtained. Although sulfur reducers could not be identified in this study, Geobacter and Desulfomicrobium were the most likely sulfur reducers. This work suggests that elemental sulfur can serve as an electron acceptor in the new high-rate anaerobic sulfidogenic process for sludge-minimized wastewater treatment. [ABSTRACT FROM AUTHOR]

Effectiveness of ultrasonication, microwave technologies, and enzyme addition prior to anaerobic digestion is investigated using sludge samples taken from the secondary settling tank of a domestic wastewater treatment plant to improve methane production, enhance dewaterability characteristics of the sludge, and to reduce excess sludge. Microwave pre‐treatment (1500 W, 10 min at 175 °C) results in better extra digester performance (compared to the control reactor) in terms of methane production (25 m3 ton−1 suspended solids (SS)) than ultrasound (no improvement) and enzyme pre‐treatment (11 m3 ton−1 SS). While methane production is not improved as a result of ultrasonication pre‐treatment (15 000 kJ kg−1 SS), a noticeable increase (19%) is observed in the case of microwave pre‐treatment. Higher compactibility values are obtained after ultrasonication and microwave application compared to the control (i.e., from 7.1 to 8.7 and 9.2%, respectively) before anaerobic digestion. Although ultrasonication and microwave application decrease the dewaterability of the raw sludge (capillary suction time (CST) from 827 to 1364 and 2290 s, respectively), similar dewaterability results are obtained at the end of the anaerobic digestion process for all pre‐treated sludge samples. An economic assessment of this study shows that pre‐treatment with microwave results in more than 10‐fold less net cost compared to the enzyme application. [ABSTRACT FROM AUTHOR]

This paper is aimed at evaluating, from a techno-economic and environmental point of view, the performance of an existing wastewater treatment plant in which the traditional biological section is upgraded with an innovative Sequencing Batch Biofilter Granular Reactor. Two scenarios were simulated in order to model and assess the performances of conventional (CAS, Conventional Activated Sludge) and innovative solutions, based on mass balances, techno-economic evaluation and environmental assessment. The results showed that converting the activated sludge process into an SBBGR allows to achieve a drastic reduction in sludge production (up to 75% as volatile suspended solids). Furthermore, the secondary sedimentation and sludge stabilization units can be dismissed, reducing the area requirement (up to 50%). The technical assessment is mainly positive, with the electric energy consumption being the only critical item. The higher energy demand of the upgraded plant (about 25% more than the conventional treatment) is mainly associated with the recycle flow in the SBBGR system. Although the economic sustainability of the upgraded plant depends on local conditions, it can be considered to be likely favourable: sludge disposal and materials & reagents costs, together with the investment for plant reconstruction are those items that should be carefully evaluated before upgrading the CAS plant with SBBGR technology. The environmental assessment shows also mostly positive results, although it points to the increased phosphorus concentration in the effluent as a potentially critical issue and it highlights the electricity use and the increased nitrous oxide generation as other matters that need to be carefully checked in real case application. [ABSTRACT FROM AUTHOR]

The feasibility of sludge reduction via the XE biodegradation process was explored both experimentally and through modeling, where the main focus was on determining the value of the bE parameter (first order degradation of XE) from a continuous process. Two activated sludge (AS) systems (30 L) were operated in parallel with synthetic wastewater during 16 months: a conventional activated sludge (CAS) system and a modified low-sludge production activated sludge (LSP-AS) process equipped with a side-stream digester unit (DU). First, the long term data of the CAS reactor (1 year) were used to calibrate the ASM model and to estimate the heterotrophic decay constant of the cultivated sludge (bH = 0.29 d-1, death-regeneration basis). Second, pre-simulations were performed to design the LSP-AS system and to estimate the DU volume required (40 L), to avoid XE accumulation in the process. Third, the LSP-AS process was built, put in operation and monitored for more than 9 months. This allowed assessment of the actual behavior of the quasi-complete solids retention system. Once calibrated, the modified AS model estimated the value of the bE parameter to be in the range of 0.003-0.006 d-1, satisfactorily describing the overall sludge yield reduction of up to 49% observed in the experiments. [ABSTRACT FROM AUTHOR]

The increase of sewage sludge production together with the high treatment and disposal costs in the last years has pushed to study different solutions aimed at sludge minimization. In this paper, the thermophilic membrane technology was evaluated as an alternative for municipal sewage sludge reduction. The experimentation (carried out by means of a pilot scale plant, 1 m 3 volume) was divided into two steps: the first one was aimed at confirming the results obtained in a previous research focused on industrial sludge treatment; the second step was devoted to define the best process conditions (in particular the optimization of the aeration phases) and to the chemical permeate characterization. The results of the experiments highlight that the hydraulic retention time (HRT) and aeration conditions play a crucial role on the overall process performance. The volatile suspended solids removal efficiency was greater than 80% under the following conditions: HRT even lower than 15 d; 2 h of aeration - 6 h of non aeration cycles; and organic loading rate of 2.0 kgCOD m −3 d −1 . The permeate showed a good biodegradability under mesophilic conditions thus being treatable by means of conventional biological processes. Moreover, ammonia (the permeate presenting high concentrations) could be recovered as a fertilizer (stripping and subsequent washing of the exhausted gas is an established technique). Finally, the ammonia-free permeate can be valorised as a carbon source in denitrification processes. [ABSTRACT FROM AUTHOR]

Foam formation in the excess sludge treatment facilities of biological wastewater treatment plants (WWTPs) may represent a critical issue as it could lead to several operative problems and reduce the overall plant performance. This trouble also affects a novel technology recently proposed for sludge minimization, the thermophilic membrane reactor (TMR), operating with alternate aeration/non-aeration cycles. This technology, which has proven to be extremely resilient and suitable for treating industrial wastewater of different nature, demonstrated a high potential also as a solution for integrating existing WWTPs, aiming at the 'zero sludge production.' In this work, an experimental study was conducted with a TMR pilot plant (fed daily with thickened sewage sludge) by adjusting the duration of aeration/non-aeration alternate cycles. Extracellular polymeric substance (EPS) concentration (and its soluble and bound fractions) has been monitored along with foaming power indices. The results highlight that foaming can be correlated to the presence of soluble protein fraction of EPS. Moreover, EPS production seems to be reduced by increasing the duration of the non-aeration cycles: optimal operating conditions resulted 2 h of aeration followed by 6 h of non-aeration. These conditions allow to obtain an EPS concentration of 500 mg L with respect to 2300 mg L measured at the beginning of experimental work. [ABSTRACT FROM AUTHOR]

Recently, the S ulfate reduction A utotrophic denitrification N itrification I ntegrated (SANI ® ) process was developed for the removal of organics and nitrogen with sludge minimization in the treatment of saline sewage (with a Sulfate-to-COD ratio > 0.5 mg SO 4 2− -S/mg COD) generated from seawater used for toilet flushing or salt water intrusion. Previously investigated in lab- and pilot-scale, this process has now been scaled up to a 800–1000 m 3 /d full-scale demonstration plant. In this paper, the design and operating parameters of the SANI demo plant built in Hong Kong are analyzed. After a 4-month start-up period, a stable sulfur cycle-based biological nitrogen removal system having a hydraulic retention time (HRT) of 12.5 h was developed, thereby reducing the amount of space needed by 30–40% compared with conventional activated sludge (CAS) plants in Hong Kong. The demo plant satisfactorily met the local effluent discharge limits during both the summer and winter periods. In winter (sewage temperature of 21 ± 1 °C), the maximum volumetric loading rates for organic conversion, nitrification, and denitrification were 2 kg COD/(m 3 ·d), 0.39 kg N/(m 3 ·d), and 0.35 kg N/(m 3 ·d), respectively. The biological sludge production rate of SANI process was 0.35 ± 0.08 g TSS produced /g BOD 5 (or 0.19 ± 0.05 g TSS/g COD), which is 60–70% lower than that of the CAS process in Hong Kong. While further process optimization is possible, this study demonstrates the SANI process can be potentially implemented for the treatment of saline sewage. [ABSTRACT FROM AUTHOR]

The sludge disintegration technologies integrated into sludge handling units are pretreatment processes that reduce the sludge mass or to improve the sludge characteristics. The sludge disintegration technologies developed to reduce excess sludge are classified as mechanical disintegration, thermal disintegration, chemical or thermo-chemical disintegration, and biological disintegration. The integration of lab/pilot/full-scale applications of these technologies into sludge handling units have been shown to significantly minimize sludge. The sludge disintegration technologies are considered to be environmentally safe because these technologies produce no environmentally harmful additional waste. Therefore, sludge minimization has received steadily increasing attention in the last few decades. Here, an overview is presented of the most widely known sludge disintegration technologies that can be integrated into sludge handling units for sludge minimization. The latest applications of sludge disintegration technologies that have been reported in the literature are comprehensively evaluated in terms of sludge solubilization, dewaterability, pathogen removal, and sludge digestibility. [ABSTRACT FROM AUTHOR]

A sludge collection tank was set up for the sludge return process of a conventional activated sludge (CAS) process. Lysozymes were then added into the sludge collection tank. The present study investigated the sludge reduction effect and the capacity for treating pollutants and analysed the possible causes behind the sludge reduction. The results show that when the sludge load was 0.5 kg (chemical oxygen demand)/kg (mixed liquor suspended solids)∙d, the amount of the excess sludge in the system with added lysozymes reduced by 37.33% compared with the amount of the excess sludge in the CAS system; in addition, the efficiency of the system with added lysozymes to treat organic compounds did not decrease due to the addition of lysozymes. An analysis of the causes for the sludge reduction shows that the energy uncoupling that occurred due to the alternation of the aerobic and anaerobic conditions of the sludge in the system with added lysozymes had almost no impact on reducing the amount of sludge in the system; the increase in the activity of the sludge in the system as well as the enhancement in the endogenous metabolic capacity caused the sludge reduction. Denaturing gradient gel electrophoresis analysis shows that there was no significant difference in the microbial diversity between the system with added lysozymes and the CAS system, which indicates that the lysozymes did not promote the reduction in the sludge yield by altering the microbial community structure in the activated sludge system. Compared with the oxic-settlinganaerobic sludge reduction system, strict anaerobic operating conditions for the sludge collection tank were not required for the system with added lysozymes, and the residence time of the sludge in the sludge collection tank was nevertheless significantly reduced, which is an advantage for the practical application of sludge reduction. [ABSTRACT FROM AUTHOR]

This study was performed to identify suitable conditions for the in-situ reduction of excess sludge production by intercalated digesters in recycle-activated sludge (RAS) flow. The objective was to compare and model biological sludge mass reduction and the biodegradation of endogenous residues ( X P ) by digestion under hypoxic, aerobic, anaerobic, and five intermittent-aeration conditions. A mathematical model based on the heterotrophic endogenous decay constant ( b H ) and including the biodegradation of X P was used to fit the long-term data from the digesters to identify and estimate the parameters. Both the b H constant (0.02–0.05 d −1 ) and the endogenous residue biodegradation constant ( b P , 0.001–0.004 d −1 ) were determined across the different mediums. The digesters with intermittent aeration cycles of 12 h–12 h and 5 min–3 h (ON/OFF) were the fastest, compared to the aerobic reactor. The study provides a basis for rating RAS-digester volumes to avoid the accumulation of X P in aeration tanks. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the ability of the oxic-settling-anaerobic (OSA)-process and the folic acid addition applied in the activated sludge process to reduce the excess sludge production. The study was monitored during two distinct periods: activated sludge system with OSAprocess, and activated sludge system with folic acid addition. The observed sludge yields (Yobs) were 0.30 and 0.08 kg TSS kg-1 chemical oxygen demand (COD), control phase and OSA-process (period 1); 0.33 and 0.18 kg TSS kg-1 COD, control phase and folic acid addition (period 2). The Yobs decreased by 73 and 45% in phases with the OSA-process and folic acid addition, respectively, compared with the control phases. The sludge minimization alternatives result in a decrease in excess sludge production, without negatively affecting the performance of the effluent treatment. [ABSTRACT FROM AUTHOR]

In the frame of a modern waste management, an important sector concerns the sewage sludge minimization. In recent years a lot of techniques have been developed to reduce the sludge production such as biological, thermal, thermochemical, high-temperature oxidation and mechanical treatments, ultrasonication and ozonation, or using chemical compounds. Among those, the use of an anaerobic side-stream reactor (ASSR) in the conventional activated sludge line is a challenging biological technology able to minimize sludge production in wastewater treatment plants. The ASSR can be easily realized in both new and existing plants as it consists of an ASSR for sludge treatment and reduction where a portion or, in some cases, all the return sludge of the activated sludge process is subjected to alternating aerobic, anoxic, and anaerobic conditions. Studies show that, combining a conventional activated process with an ASSR, sludge yield could be reduced by up to 40–60% without any negative effects, neither on the effluent quality nor on the settling characteristics of the activated sludge. The process has been applied using various configurations. Further, different explanations about the reduction mechanisms behind the process have been provided. This article is a review of the existing applications of the ASSR in laboratory scale and patents in order to describe the configurations implemented, the performance of the process in terms of sludge reduction and carbon and nutrients removal, the main operative parameters, and the mechanisms of sludge reduction observed. [ABSTRACT FROM AUTHOR]

In the last years, sewage sludge management turned out to be a topic of great interest due to the increasing sludge production and the high cost of sludge treatment and disposal. In this context, several methods are being studied for sewage sludge minimization: among them, wet oxidation (WO) was proposed as an effective hydrothermal oxidation based technology. The aim of this work, carried out within the European project “ROUTES,” was the assessment of the influence of sludge composition on process performance: for this purpose, seven different types of sewage sludge were submitted to WO tests at lab scale. Moreover, each operating condition (temperature, reaction time, and initial oxygen pressure) was varied so as to highlight the effect of process parameters on oxidation efficiency; this was essentially evaluated in terms of chemical oxygen demand (COD), volatile suspended solid (VSS) and total suspended solid (TSS) reduction. COD and VSS abatement varied in the ranges 44–85%, 71–99% depending on reaction time (15–120 min) and 22–79%, 54–99% as a function of temperature (200–250°C), respectively. Furthermore, by comparing WO tests results of the seven types of sludge obtained under the same treatment conditions (temperature = 250°C and reaction time = 60 min), it was highlighted that VSS and COD removal efficiency can be correlated to the initial VSS/TSS ratio. [ABSTRACT FROM PUBLISHER]

Dynamic activated sludge modeling (ASM) and the concept of chemical oxygen demand fractionation utilized by this modeling approach suggested the existence of new strategies for minimization of excess sludge. One of these strategies consists of eliminating the traditional sludge wastage (WAS) and avoiding the buildup of inert solids in the aeration tanks by other means: fine screens are used to remove the inert particulate organic fraction (XI), hydrocyclones (HC) are used for inorganic suspended solids (ISS), and different types of online digesters are used to further biodegrade the endogenous residues (XP) via the return activated sludge (RAS) line. In this research, a model and a simulation program were developed that were able to mimic the apparent behavior of activated sludge variants with low solids production (LSP-AS). The model is an extended ASM1 assuming a small first-order biodegradation constant forXP = 0.007 d−1), and black boxes representXIand ISS removal. The simulations first depicted the way that different solid components build up in the aeration tanks when traditional activated sludge (C-AS) is operated at very high solids retention times (>100 d, without sieves and HC). Secondly, the modeling showed that the C-AS process could hypothetically be replaced by LSP-AS variants with similar levels of active biomass and mixed liquor total suspended solids in the aeration tanks (2,500–3,500 mg L−1TSS). For the studied case, at least 2 and 6% of the RAS flow must be screened and digested, respectively, to avoid the accumulation ofXI, ISS, andXP. Additionally, the size of the online digester will be approximately twice the volume of the aeration tank. The mathematical model implemented in Aquasim could serve as a didactical, operational, and research simulation tool for LSP activated sludge processes. [ABSTRACT FROM AUTHOR]

The management of sewage sludge is becoming a more and more important issue, both at national and international level, in particular due to the uncertain recovery/disposal future options. Therefore, it is clear that the development of new technologies that can mitigate the problem at the source by reducing sludge production is necessary, such as the European Directive 2008/98/EC prescribes. This work shows the results obtained with a thermophilic membrane reactor, for processing a biological sludge derived from a wastewater treatment plant (WWTP) that treats urban and industrial wastewater. Sewage sludge was treated in a thermophilic membrane reactor (TMR), at pilot-scale (1 m 3 volume), with alternate aeration cycles. The experimentation was divided into two phases: a “startup phase” during which, starting with a psychrophilic/mesophilic biomass, thermophilic conditions were progressively reached, while feeding a highly biodegradable substrate; the obtained thermophilic biomass was then used, in the “regime phase”, to digest biological sludge which was fed to the plant. Good removal yields were observed: 64% and 57% for volatile solids (VS) and total COD (COD tot ), respectively, with an average hydraulic retention time (HRT) equal to 20 d, an organic loading rate (OLR) of about 1.4–1.8 kg COD m −3 d −1 and aeration/non aeration cycles alternated every 4 h. [ABSTRACT FROM AUTHOR]

The activated sludge process is the most widely used treatment method for municipal wastewater. However, the excessive amount of biomass generated during the process is a major drawback. Earlier studies using the activated sludge process running in a biomass fasting and feasting mode demonstrated both nutrient removal and a minimization of biomass production. However, these studies were conducted using synthetic wastewater. In this study, we report findings from a lab-scale sludge-minimizing biological nutrient removing (BNR) reactor when its operation was changed from synthetic to real wastewater (primary effluent). Two lab-scale sequencing batch reactors, one in sludge minimization mode (hereafter called modified-SBR), and the other in conventional activated sludge mode (referred as control-SBR), were operated for more than 300 days. Both reactors were started and operated with synthetic feed. Gradually the feed to both reactors was changed to 100% primary effluent collected from a local full-scale wastewater treatment plant. Irrespective of the feed composition, more than 98% NH 3 –N removal was recorded in both SBRs. However, while 89% of the total dissolved phosphorus was removed from the 100% synthetic feed, only 80% of the total dissolved phosphorus was removed from the 100% primary effluent in both SBRs. The overall observed sludge reduction in the modified-SBR as compared to the control-SBR also decreased from 65% to 39% when the feed was changed from 100% synthetic to 100% primary effluent. The specific oxygen uptake rate for the modified-SBR was 80% higher than that for the control-SBR when the SBRs were fed with primary effluent wastewater. The modified-SBR showed a greater diversity of ammonia-oxidizing bacteria (AOBs) with synthetic wastewater as well as during the transition period than the control-SBR. Yet when the reactors were running on 100% real wastewater, only Nitrosomonas europaea / eutropha were identified in both SBRs. The nitrite-oxidizing bacterial community and the polyphosphate accumulating organisms (PAOs) responded in a similar way in both SBRs. [ABSTRACT FROM AUTHOR]

Reducing excess sludge production is increasingly attractive as a result of rising costs and constraints with respect to sludge treatment and disposal. A technology in which the mechanisms remain not well understood is the Cannibal process, for which very low sludge yields have been reported. The objective of this work was to use modeling as a means to characterize excess sludge production at a fullscale Cannibal facility by providing a long sludge retention time and removing trash and grit by physical processes. The facility was characterized by using its historical data, from discussion with the staff and by conducting a sampling campaign to prepare a solids inventory and an overall mass balance. At the evaluated sludge retention time of 400 days, the sum of the daily loss of suspended solids to the effluent and of the waste activated sludge solids contributed approximately equally to the sum of solids that are wasted daily as trash and grit from the solids separation module. The overall sludge production was estimated to be 0.14 g total suspended solids produced/g chemical oxygen demand removed. The essential functions of the Cannibal process for the reduction of sludge production appear to be to remove trash and grit from the sludge by physical processes of microscreening and hydrocycloning, respectively, and to provide a long sludge retention time, which allows the slow degradation of the "unbiodegradable" influent particulate organics (XUInf) and the endogenous residue (XE). The high energy demand of 1.6 kWh/m³ of treated wastewater at the studied facility limits the niche of the Cannibal process to small- to mediumsized facilities in which sludge disposal costs are high but electricity costs are low. [ABSTRACT FROM AUTHOR]

Nowadays, sewage sludge management represents one of the most important issues in wastewater treatment. Within the European project 'ROUTES,' wet oxidation (WO) was proposed for sludge minimization. Four different types of sludge were treated in an industrial WO plant: (1) municipal primary sludge (chemical oxygen demand COD: 73.0 g/L; volatile suspended solid VSS: 44.1 g/L); (2) secondary sludge from an industrial wastewater treatment plant (WWTP) without primary sedimentation (COD: 71.8 g/L; VSS: 34.2 g/L); (3) secondary sludge from a mixed municipal and industrial WWTP without primary sedimentation (COD: 61.9 g/L; VSS: 38.7 g/L); and (4) mixed primary (70 %) and secondary (30 %) municipal sludge (COD: 81.2 g/L; VSS: 40.6 g/L). The effect of process parameters (temperature, reaction time, oxygen dosage) on WO performance was investigated. Depending on operating conditions, VSS and COD removal efficiency varied in the range 80-97 % and 43-71 %, respectively. A correlation between process efficiency and the initial VSS/TSS (total suspended solids) ratio was highlighted. Furthermore, a mathematical model of WO process for simulating VSS and COD profiles was developed. [ABSTRACT FROM AUTHOR]

This paper describes the preliminary assessment of a platform of innovative upgrading solutions aimed at improving sludge management and resource recovery in wastewater treatment plants. The effectiveness of the upgrading solutions and the impacts of their integration in model reference plants have been evaluated by means of mass and energy balances on the whole treatment plant. Attention has been also paid to the fate of nitrogen and phosphorus in sludge processing and to their recycle back to the water line. Most of the upgrading options resulted in reduced production of dewatered sludge, which decreased from 45 to 56 g SS/(PE × day) in reference plants to 14-49 g SS/(PE × day) in the upgraded ones, with reduction up to 79 % when wet oxidation was applied to the whole sludge production. The innovative upgrades generally entail an increased demand of electric energy from the grid, but energy recovery from biogas allowed to minimize the net energy consumption below 10 kWh/(PE × year) in the two most efficient solutions. In all other cases the net energy consumption was in the range of −11 % and +28 % of the reference scenarios. [ABSTRACT FROM AUTHOR]

Excess sludge production in wastewater treatment plants has become an enormous environmental issue worldwide mainly due to the increased efforts towards wastewater purification. Researchers and plant operators are looking for technological solutions to reduce sludge production through the upgrading of existing technologies and configurations or by substituting them with alternative solutions. Several strategies have been identified to reduce sludge production, including the use of biological and physical-chemical methods (or a combination of them) and novel technologies, although many have not been sufficiently tested at full-scale. To select the most suitable system for sludge reduction, understanding the reduction mechanisms, advantages, disadvantages, and the economic and environmental impact of each technology is essential. This work offers a comprehensive and critical overview of mainstream sludge reduction technologies and underlying mechanisms from laboratory to full scale, and describes potential application, configuration, and integration with conventional systems. Research needs are highlighted, and a techno-economic-environmental comparison of the existing technologies is also proposed. [Display omitted] • Mainstream technologies and mechanisms for sludge reduction are critically reviewed. • Endogenous metabolism and cell lysis are the most applied minimization mechanisms. • Upgrade of conventional systems with anaerobic reactors reduces sludge production. • Granular sludge and membrane systems feature the lowest biomass yields. • Physical-chemical treatments are coupled to biosystems to improve sludge reduction. [ABSTRACT FROM AUTHOR]

In the present work we studied the thermophilic biological treatability of high strength liquid wastes from a pharmaceutical industry (rich in organic matter - COD: Chemical Oxygen Demand, nutrients and salinity). Different mixtures (with concentrations of COD, phosphorus and chloride up to 57,000 mg L-1, 2000 mg L-1 and 9000 mg L-1, respectively) were tested. The pilot plant used in this work was designed and built with dimensions comparable to a semi-industrial unit. The results are therefore representative for full-scale applications. During four months of experimentation, the pilot plant (TAMR - Thermophilic Aerobic Membrane Reactor) was operated at 49 ± 1 °C and the organic loading rate was 1.5-5.5 kgCOD m-3 d-1 with a hydraulic retention time of 5-10 days. Main results are the following: a) extremely high COD removal rate (up to 98%); b) very low sludge production (~0.016 kgVSS produced kgCOD removed-1); c) suitability as a pre-treatment to a conventional (e.g. activated sludge) biological treatment (the studied pharmaceutical industrial wastewaters are discharged into the sewer system for final polishing in a centralized municipal wastewater treatment plant) and d) high phosphorus removal (up to 99%). [ABSTRACT FROM AUTHOR]

BACKGROUND For the first time, low intensity ultrasonication was applied to stimulate biological activities during aerobic digestion of municipal waste activated sludge (AS). Specific oxygen uptake rate (SOUR) analysis was performed to investigate the sono-biostimulation effects on AS activity. RESULTS The greatest improvement of 60% in SOUR was observed at sonication density and irradiation time of 0.2 W mL-1 and 60 s, respectively. A subsequent batch aerobic digestion study showed 74% reduction in total chemical oxygen demand (TCOD) and volatile suspended solids (VSS) after 12 days of aerobic digestion, with 127% and 112% improvement in TCOD and VSS removal, respectively, in comparison with the control reactor. The sono-biostimulation effects on AS lasted 6 h and completely disappeared within 8 h after sonication stopped. CONCLUSIONS The sonication density, irradiation time and volume and frequency of sludge sonication were observed to play important roles in bio-stimulation and the subsequent aerobic digestion process. Intermittent sonication protocol for 60 s every 8 h was the best treatment condition to improve aerobic digestion efficiency. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Solids reduction in activated sludge processes (ASP) at source using process manipulation has been researched widely over the last two-decades. However, the absence of nutrient removal component, lack of understanding on the organic carbon, and limited information on key microbial community in solids minimizing ASP preclude the widespread acceptance of sludge minimizing processes. In this manuscript, we report simultaneous solids reduction through anaerobiosis along with nitrogen and phosphorus removals. The manuscript also reports carbon mass balance using stable isotope of carbon, microbial ecology of nitrifiers and polyphosphate accumulating organisms (PAOs). Two laboratory scale reactors were operated in anaerobic-aerobic-anoxic (A2O) mode. One reactor was run in the standard mode (hereafter called the control-SBR) simulating conventional A2O type of activated sludge process and the second reactor was run in the sludge minimizing mode (called the modified-SBR). Unlike other research efforts where the sludge minimizing reactor was maintained at nearly infinite solids retention time (SRT). To sustain the efficient nutrient removal, the modified-SBR in this research was operated at a very small solids yield rather than at infinite SRT. Both reactors showed consistent NH3–N, phosphorus and COD removals over a period of 263 days. Both reactors also showed active denitrification during the anoxic phase even if there was no organic carbon source available during this phase, suggesting the presence of denitrifying PAOs (DNPAOs). The observed solids yield in the modified-SBR was 60% less than the observed solids yield in the control-SBR. Specific oxygen uptake rate (SOUR) for the modified-SBR was almost 44% more than the control-SBR under identical feeding conditions, but was nearly the same for both reactors under fasting conditions. The modified-SBR showed greater diversity of ammonia oxidizing bacteria and PAOs compared to the control-SBR. The diversity of PAOs in the modified-SBR was even more interesting in which case novel clades of Candidatus Accumulibacter phosphatis (CAP), an uncultured but widely found PAOs, were found. [Copyright &y& Elsevier]

Minimization of excess sludge production may be achieved by either changes in operational conditions or by the treatment of recycled activated sludge. It was investigated using ozone-treated return activated sludge in lab-scale activated sludge process operated continuously with optimum conditions determined using Box-Behnken experimental design method as 400 mg/L initial chemical oxygen demand concentration (CODi), 25 h hydraulic retention time, and 25 d solid retention time, respectively. Batch experiments were carried out in order to determine the optimum ozone dose of 0.05 gO3/g total solid considering disintegration degree (DD). Ozone reactor (OR) and control reactor (CR) were evaluated considering sludge reduction capacity, effluent quality, and sludge characteristics. About 61 and 40% reductions can be achieved in mixed liquor suspended solid concentration and observed sludge yield value in OR compared to CR, respectively. The effluent quality in terms of COD and NH4-N removal in OR was not significantly affected by ozonation. The dewatering capacity was slightly weakened while little improvement was observed in filtering capacity in OR compared to CR, in terms of capillary suction time and specific resistance to filtration. Particle size changed and sludge destruction led to an increase of small particles. [ABSTRACT FROM AUTHOR]

Abstract: This paper is designed to critically review the recent developments of membrane bio-technologies for sludge reduction and treatment by covering process fundamentals, performances (sludge reduction efficiency, membrane fouling, pollutant removal, etc.) and key operational parameters. The future perspectives of the hybrid membrane processes for sludge reduction and treatment are also discussed. For sludge reduction using membrane bioreactors (MBRs), literature review shows that biological maintenance metabolism, predation on bacteria, and uncoupling metabolism through using oxic-settling-anaerobic (OSA) process are promising ways that can be employed in full-scale applications. Development of control methods for worm proliferation is in great need of, and a good sludge reduction and MBR performance can be expected if worm growth is properly controlled. For lysis-cryptic sludge reduction method, improvement of oxidant dispersion and increase of the interaction with sludge cells can enhance the lysis efficiency. Green uncoupler development might be another research direction for uncoupling metabolism in MBRs. Aerobic hybrid membrane system can perform well for sludge thickening and digestion in small- and medium-sized wastewater treatment plants (WWTPs), and pilot-scale/full-scale applications have been reported. Anaerobic membrane digestion (AMD) process is a very competitive technology for sludge stabilization and digestion. Use of biogas recirculation for fouling control can be a powerful way to decrease the energy requirements for AMD process. Future research efforts should be dedicated to membrane preparation for high biomass applications, process optimization, and pilot-scale/full-scale tracking research in order to push forward the real and wide applications of the hybrid membrane systems for sludge minimization and treatment. [Copyright &y& Elsevier]

Lysozyme reaction was developed as a novel technique for minimizing the amount of excess sludge in the sequential batch reactor (SBR). In the present work, excess sludge taken from a SBR system was treated by lysozyme reaction and then returned to the reactor. The quality of the effluent water and characteristics of the activated sludge in the SBR were analyzed to determine the effectiveness of the reduction process. The results show that excess sludge production could be reduced to almost 100% in the first 30 d of operation and could be reduced to further by 40% in the succeeding 20 d or so. In these time periods, the average removal efficiencies of the chemical oxygen demand and total nitrogen are 87.38% and 52.78%, respectively, whereas the average total phosphorous in the effluent is nearly 17.18% greater than that of the effluent of the reference system. After 50 d of operation, the sludge floc size is in the range of 20 to 80 μm, which was smaller than the size prior to the start of the hydrolysis and the ratio of mixed liquor volatile suspended solids/mixed liquor suspended solids increases from 86% to 90%. [ABSTRACT FROM AUTHOR]

Saline water supply has been successfully practiced for toilet flushing in Hong Kong since 1950s, which saves 22% of freshwater in Hong Kong. In order to extend the benefits of saline water supply into saline sewage management, we have recently developed a novel biological organics and nitrogen removal process: the Sulfate reduction, Autotrophic denitrification, and Nitrification Integrated (SANI®) process. The key features of this novel process include elimination of oxygen demand in organic matter removal and production of minimal sludge. Following the success of a 500-day lab-scale trial, this study reports a pilot scale evaluation of this novel process treating 10 m3/day of 6-mm screened saline sewage in Hong Kong. The SANI® pilot plant consisted of a sulfate reduction up-flow sludge bed (SRUSB) reactor, an anoxic bioreactor for autotrophic denitrification and an aerobic bioreactor for nitrification. The plant was operated at a steady state for 225 days, during which the average removal efficiencies of both chemical oxygen demand (COD) and total suspended solids (TSS) at 87% and no excess sludge was purposefully withdrawn. Furthermore, a tracer test revealed 5% short circuit flow and a 34.6% dead zone in the SRUSB, indicating a good possibility to further optimize the treatment capacity of the process for full-scale application. Compared with conventional biological nitrogen removal processes, the SANI® process reduces 90% of waste sludge, which saves 35% of the energy and reduces 36% of fossil CO2 emission. The SANI® process not only eliminates the major odor sources originating from primary treatment and subsequent sludge treatment and disposal during secondary saline sewage treatment, but also promotes saline water supply as an economic and sustainable solution for water scarcity and sewage treatment in water-scarce coastal areas. Biotechnol. Bioeng. 2012; 109: 2778-2789. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The excess biomass produced during biological treatment of municipal wastewater represents a major issue worldwide, as its disposal implies environmental, economic and social impacts. Therefore, there has been a growing interest in developing technologies to reduce sludge production. The main proposed strategies can be categorized according to the place inside the wastewater treatment plant (WWTP) where the reduction takes place. In particular, sludge minimization can be achieved in the wastewater line as well as in the sludge line. This paper presents the results of two pilot scale systems, to evaluate their feasibility for sludge reduction and to understand their effect on biomass activity: (1) a pilot plant with an ozone contactor in the return activated sludge (RAS) stream for the exposition of sludge to a low ozone dosage; and (2) an oxicsettling-anaerobic (OSA) process with high retention time in the anaerobic sludge holding tank have been studied. The results showed that both technologies enabled significant excess sludge reduction but produced a slight decrease of biomass respiratory activity. [ABSTRACT FROM AUTHOR]

Abstract: The Activated Sludge Model No. 2d (ASM2d) was extended to incorporate the processes of both predation and viral infection. The extended model was used to evaluate the contributions of predation and viral infection to sludge minimization in a sequencing batch reactor (SBR) system enriching polyphosphate-accumulating organisms (PAOs). Three individual decay processes formulated according to the general model rules were used in the extended model. The model was firstly calibrated and validated by different experimental results. It was used to evaluate the potential extent of predation and viral infection on sludge minimization. Simulations indicate that predation contributes roughly two times more to sludge minimization than viral infection in the SBR system enriching PAOs. The sensitivity analyses of the selected key parameters reveal that there are thresholds on both predation and viral infection rates, if they are too large a minimal sludge retention time is obtained and the effluent quality is deteriorating. Due to the thresholds, the contributions of predation and viral infection to sludge minimization are limited to a maximal extent of about 21% and 9%, respectively. However, it should be noted that the parameters concerning predation and viral infection were not calibrated separately by independent experiment in our study due to the lack of an effective method, especially for the parameters regarding viral infection. Therefore, it is essential to better evaluate these parameters in the future. [Copyright &y& Elsevier]

In this study, high-solids anaerobic digestion of thermally pretreated wastewater solids (THD) was compared with conventional mesophilic anaerobic digestion (MAD). Operational conditions, such as pretreatment temperature (150 to 170°C), solids retention time (15 to 20 days), and digestion temperature (37 to 42°C), were varied for the seven THD systems operated. Volatile solids reduction (VSR) by THD ranged from 56 to 62%, compared with approximately 50% for MAD. Higher VSR contributed to 24 to 59% increased biogas production (m³/kg VSR·d) from THD relative to MAD. The high-solids conditions of the THD feed resulted in high total ammonia-nitrogen (proportional to solids loading) and total alkalinity concentrations in excess of 14 g/L as calcium carbonate (CaCO3). Increased pH in THD reactors caused 5 to 8 times more un-ionized ammonia to be present than in MAD, and this likely led to inhibition of aceticlastic methanogens, resulting in accumulation of residual volatile fatty acids between 2 and 6 g/L as acetic acid. The THD produced biosolids cake that possessed low organic sulfur-based biosolids odor and dewatered to between 33 and 39% total solids. Dual conditioning with cationic polymer and ferric chloride was shown to be an effective strategy for mitigating dissolved organic nitrogen and UV-quenching compounds in the return stream following centrifugal dewatering of THD biosolids. [ABSTRACT FROM AUTHOR]

In this research, possibility of reducing excess sludge production in wastewater treatment was investigated using a combined anaerobic and aerobic submerged biological filter in a pilot scale. The physical model designed, erected and operated consisted of two pipes of PVC type with 147mm and 237mm diameter used as aerobic and anaerobic filters, respectively. The effective height of porous media in these filters was 70cm. Two filters were connected to eachother in a series form and the resulted system was loaded using synthetic wastewater based on sucrose in the range of 1.91 to 30.61 kg/m3 for anaerobic filter and 1.133 to 53.017 kg/m3 for aerobic filter. For similar loadings, the aerobic filter showed efficiency of 1.8 times that of anaerobic filter in removal of soluble COD. Return of 100% flow from the aerobic filter to the anaerobic filter for 30kg/m3.d of organic loading increased the efficiencies of the anaerobic filter, the aerobic filter and the combined system as 17%, 14% and 15%, respectively and the effect of the return of the flow was more pronounced in smaller hydraulic retention times and larger loadings. 100% return of the flow reduced the yield coefficient for the whole system to 0.037 for 53 kg/m3 loading which is a suitable value with regard to the scheme and no use of chemical materials such as chlorine and ozone. This coefficient reached a value as small as 0.007 in common loadings (7.5kg/m3) for 100% return of the flow which is very close to zero. So, this method could be considered as a complete biological treatment with low excess sludge and could be assessed in full scale. [ABSTRACT FROM AUTHOR]

This paper presents a full-scale experience of sludge minimization by means of short contact time ozonation in a wastewater treatment plant (WWTP) mainly fed on textile wastewater. The WWTP performance over a 3-year operational data series was analysed and compared with a two-year operation with sludge ozonation. Lab-scale respirometric tests were also performed to characterize biomass activity upstream and downstream of the ozone contact reactor. Results suggest that sludge ozonation: (1) is capable of decreasing excess sludge production by 17%; (2) partially decreases both N removal, by lowering the denitrification capacity, and P removal, by reducing biomass synthesis; (3) increases the decay rate from the typical value of 0.62 d-1 to 1.3 d-1; (4) decreases the heterotrophic growth yield from the typical value of 0.67 to 0.58 gCOD/gCOD. [ABSTRACT FROM AUTHOR]

Abstract: In this study ultrasonic pretreatment was investigated in order to improve anaerobic digestion. First, the most effective sonication time was selected during the preliminary studies conducted on waste activated sludge samples. Then the optimal time selected was confirmed running batch anaerobic reactors. In the last part of the experiments, the effect of sonication was investigated for different operational conditions of semi-continuous digesters. Preliminary studies showed 15min of sonication increased 50mg/L initial soluble COD concentration up to a value of 2500mg/L. Batch anaerobic digester results indicated that the increased soluble substrate improved anaerobic biodegradability concurrently, again with the maximal improvement observed for 15min of sonication. Results from semi-continuous reactors indicated that at SRT of 15days and OLR of 0.5kg/m3 d, ultrasonic pretreatment improved the daily biogas production, methane production and volatile solids reduction significantly when compared to control system. During the operation of reactors at 7.5days of SRT, pretreatment helped to keep the reactors working. A simple economical analysis of the system was performed using the data obtained during the laboratory study. [ABSTRACT FROM AUTHOR]

Abstract: Due to a high solubilization of organic matter, classical sorption models were not able to correctly describe the equilibrium of heavy metals uptake by activated sludge after disintegration processes (e.g. ultrasonic irradiation). A new semi-mechanistic model deriving from the simple Freundlich equation is developed in this study to describe metal interactions within activated sludge previously subjected to ultrasonic treatment: the equilibrium between both aqueous (complexation with soluble/colloidal organic matter released during the treatment) and particulate (sorption on sludge flocs, precipitation) metal fractions is modeled. The results of biosorption and precipitation tests were described by the new model. This allowed a better understanding of the influence of activated sludge properties (surface functional groups, structure, chemical composition) on the fate of both copper and cadmium in sonicated activated sludge. [ABSTRACT FROM AUTHOR]