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The wastewater effluent quality in BNR systems critically depends on the availability of readily biodegradable carbon source in the influent. Primary sludge in WWTPs is identified as a renewable resource for internal carbon source production. The effects of SRT, temperature and RR on the anaerobic fermentation process performance were assessed and the biological nutrient removal performance was evaluated in this study. The results showed SRT of 5d, temperature of 30°C and RR of 20 is the optimal operating condition for primary sludge anaerobic fermentation. Under the optimal operating condition, the SCOD and VFA production rate of the fermentation product is in the range of 0.39~0.48 mg SCOD/mg VSS and 0.25~0.31 mgVFA/mg VSS. The full-scale application of internal carbon source production has achieved better effluent quality (TN 7.1 mg/L and TP 0.3 mg/L) compared to the effluent (TN 18.4 mg/L and TP 1.3 mg/L) without adding carbon source. Primary sludge fermentation can be considered as an appropriate solution for carbon source production and contribute to the goal of meeting stringent wastewater discharge standard. [ABSTRACT FROM AUTHOR]

The paper presents a long-term and extensive pilot-scale study on the primary settlement of municipal sewage to produce an in-depth understanding relating sedimentation efficiency to surface load, hydraulic retention time (HRT), sludge withdrawal time (SWT), temperature (T), and influent solid mass (TSS mass). Besides, primary sludge (PS) was subject to qualitative and quantitative analysis, intending to explore its potential utilization in various applications. These applications encompass enhanced energy and heat generation through conventional anaerobic digesters and the elevated production of volatile fatty acids (VFAs) in hydrolysis reactors, particularly within the context of biorefineries. TSS mass , T, and SWT were shown to be more important in controlling the removal of solids by primary sedimentation tank (PST) than other factors considered. This study introduces a mathematical model that can predict the PS volume based on factors like TSS mass , T, and SWT as a synthesis of the two disparate facets of the study. This model can immensely help maximize PS production quantitively and qualitatively, which can help elevate energy and VFAs production from PS via anaerobic digesters and hydrolysis reactors in conventional municipal WWTP and biorefineries, respectively. Therefore, this model can confidently be applied for calculating the required hopper volume in PST and ascertaining the optimal volume specifications for anaerobic digesters and hydrolysis reactors. Consequently, it leads to cost savings associated with eliminating under or over-designing. The results showed that by improving PST performance for TSS removal, more chemical oxygen demand (COD) would be available for biogas production in conventional municipal WWTPs (from 42 to 59 g (cap. d)−1). By shifting toward biorefineries, the potential to produce more biogas and VFAs, altering from around 40–50 g (cap. d)−1 and 6–12 gVFAs (cap. d)−1, respectively, will also be indicated. [Display omitted] • In-depth analysis of the critical factors affecting the settling process in the primary sedimentation tank (PST). • Proposing a model for predicting primary sludge (PS) production by integrating the most important critical factors. • Stratification of PS to understand nutrient and carbon source variation in each layer. • Proposing reasonable sludge withdrawal time (SWT) for better running of PST and more biogas production. • Assessing improved biogas and volatile fatty acids (VFAs) production through better designing. [ABSTRACT FROM AUTHOR]

[Display omitted] • HTL potential of different WWTPs and sludge composition. • Assessment of synergistic effects of mixing WWTPs waste fractions. • Highest bio-crude yield at 325 °C for all slurry mixes. • Higher than expected bio-crude yields when mixing the feedstocks. • High energy recovery, up to 76% from mix feedstock. The rapid growth of urban populations necessitates the development of more efficient and environmentally sustainable methods for waste treatment and resource recovery. Hydrothermal liquefaction (HTL) has emerged as a promising technology for converting organic waste into bio-crude oil. In this study, the HTL products of various waste fractions (Fat, oil, and grease (FOG), food waste, primary and secondary sludge, and digestate) produced or handled by four wastewater treatment plants in Denmark were analysed. Additionally, the effect of mixing the produced waste was investigated. The HTL experiments were conducted at temperatures 300, 325, and 350 °C, with a residence time of 20 min and dry matter content of 16.7%. The highest HTL bio-crude yields were obtained at a temperature of 325 °C for all feedstocks except FOG (300 °C). The mixing of wastes resulted in a positive synergistic effect, presenting an energy recovery between 62 and 76% and bio-crude yields higher than expected due to interactions between the feedstock's biochemical composition. Based on the biochemical composition and on the feedstocks fraction, two models are proposed for the prediction of bio-crude yields, with an error between 4 and 5% in absolute terms. In addition, important process water parameters, as well as the nutrient recovery and heavy metal load of the solid residues are analysed and discussed, giving a comprehensive overview of the potential of different wastewater treatment plant sludges. [ABSTRACT FROM AUTHOR]

Abstract Dewatering and handling of pulp and paper mill sludge is challenging and often comprises more than half of the overall wastewater treatment costs at a mill. Primary sludge is usually more dewaterable than biosludge (waste activated sludge), and the ratio between both types of sludge largely determines the dewaterability of the sludge mix. This study has quantified the benefits of adding primary sludge to biosludge to enhance the dewaterability in terms of cake solids and filtrate/pressate solids content. Furthermore, the effects of the particle size distribution and the monovalent to divalent cation ratio of the various types of sludge were investigated. Biosludge and three types of primary sludge from a Canadian pulp and paper mill were mixed at various ratios and tested for dewaterability using a Crown Press®, a bench-scale device which simulates industrial belt press dewatering. Results show that after addition of primary sludge at up to 40% mass proportion (dry solids basis) the dewatered cake solids content increased substantially, from 10.4% to 18.7–19.9%, depending on the type of primary sludge added. Further addition of primary sludge led to comparably only small improvements. Primary sludge addition also resulted in decreased total suspended solids (TSS) concentrations in the combined gravity filtrate / Crown Press pressate. Primary sludge content of only 10% in the sludge mix was sufficient to decrease the TSS concentration from 1.8 g /L to 0.2 – 0.4 g /L. The study shows that only less than half of the sludge mix needs to consist of primary sludge, in order to achieve adequate dewaterability. This opens up the possibility of retaining more primary fiber within the pulping process, without compromising downstream sludge dewatering. [ABSTRACT FROM AUTHOR]

This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time (HRT) in anaerobic digesters. Initially, a batch test comparing different microalgae (untreated and pretreated) and primary sludge proportions showed how the co-digestion improved the AD kinetics. The highest methane yield was observed by adding 75% of primary sludge to pretreated microalgae (339 mL CH4/g VS). This condition was then investigated in mesophilic lab-scale reactors. The average methane yield was 0.46 L CH4/g VS, which represented a 2.9-fold increase compared to pretreated microalgae mono-digestion. Conversely, microalgae showed a low methane yield despite the thermal pretreatment (0.16 L CH4/g VS). Indeed, microscopic analysis confirmed the presence of microalgae species with resistant cell walls (i.e., Stigioclonium sp. and diatoms). In order to improve their anaerobic biodegradability, the HRT was increased from 20 to 30 days, which led to a 50% methane yield increase. Overall, microalgae AD was substantially improved by the co-digestion with primary sludge, even without pretreatment, and increasing the HRT enhanced the AD of microalgae with resistant cell walls. [ABSTRACT FROM AUTHOR]

Sewage sludge management is a problem of growing importance. Anaerobic sewage sludge stabilization is commonly used technology, where organic matter contained in primary and activated sewage sludge is converted into biogas, so both, pollution control and energy recovery can be achieved. The paper deals with the effect of process temperature (36 °C, 42 °C and 50 °C) on biogas production and quality during anaerobic stabilization of primary and activated sewage sludge generated during purifying process in low-loaded activated sludge process. Primary and activated sewage sludge samples were taken at the wastewater treatment plant Brno, Czech Republic. The characteristics of sludges (dry matter and organic dry matter content, pH, conductivity, redox potential) were dermined. Biogas production and quality was measured using 3 anaerobic systems, each of 8 batch anaerobic fermenters, at the 3 different temperature conditions 36 °C, 42 °C and 50 °C. Hydraulic retention time was 20 days. Hypothesis, which predicts that the fermentation of primary and activated sludge provides dissimilar methane quantity and quality under different temperature conditions (36 °C, 42 °C and 50 °C), was partially confirmed. Temperature 42 °C significantly increased biogas production from primary sewage sludge (by 60 % in comparison with production at 36 °C). For activated sewage sludge samples no significant influence of temperature on the biogas production was observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel primary sludge classifier (hydrocyclone) was designed and tested in this study. • CFD models were developed for different influent velocity in the activated sludge process. • The simulation and experimental classification efficiencies: 27.6% and 28.2%. • The CF's for TSS, FSS and VSS were 1.50 ± 0.18 , 1.69 ± 0.27 and 1.35. ± 0.21. • High potential of aeration energy saving: ∼3194 kWh/year (0.07 kWh/m3). The primary treatment of wastewater, which involves the sedimentation of solid debris, results in the production of primary sludge. This paper presents the computational fluid dynamics (CFD) study of the Rietema type hydrocyclone for primary sludge classification in an activated sludge process (ASP) based wastewater treatment plant. The CFD simulation of hydrocyclone was performed to study the pressure profiles (absolute pressure, total pressure), axial velocity, tangential velocity, particle track and classification efficiency for the experimental validation. The experimental values of concentration factor (CF) for total suspended solids (TSS), fixed suspended solids (FSS) and volatile suspended solids (VSS) were 1.50 ± 0.18, 1.69 ± 0.27 and 1.35 ± 0.21, respectively. The simulation and experimental classification efficiencies were 27.6% and 28.2%, respectively. Furthermore, the results of this study shows that the installation of hydrocyclone for the classification of the primary sludge saves 3194 kWh/year of energy required for wastewater treatment. [ABSTRACT FROM AUTHOR]

Five semi-continuous flow anaerobic digesters treating a mixture of food waste (FW) and municipal biosolids (primary sludge and thickened wasted activated sludge) at an solids retention time (SRT) of 20 days and different blend ratios i.e. 0, 10%, 20%, 40% by volume with the fifth digester treating only biosolids at the same COD/N ratio as the 40% FW digester were operated to investigate co-digestion performance. Sixty days of steady-state operation at organic loading rates (OLR) of 2.2–3.85 kgCOD/m 3 /d showed that COD removals were higher for the three co-digesters than for the two municipal biosolids digesters i.e. 61–69% versus 47–52%. Specific methane production per influent CODs were 1.3–1.8 folds higher in co-digestion than mono-digestion. The first-order COD degradation kinetic constants for co-digestion were more than double the mono-digestion. Additional methane production through synergism accounted for a minimum of 18–20% of the overall methane production. The estimated non-biodegradable fraction of the FW particulate COD was 7.3%. However, the co-digesters discharged 1.23–1.64 times higher soluble nitrogen than the control. [ABSTRACT FROM AUTHOR]

A novel activated primary tank process (APT) was developed for recovering carbon source by fermentation and elutriation of primary sludge. The effects of solids retention time (SRT), elutriation intensity (G) and return sludge ratio (RSR) on this recovery were evaluated in a pilot scale reactor. Results indicated that SRT significantly influenced carbon source recovery, and mechanical elutriation could promote soluble COD (SCOD) and VFA yields. The optimal conditions of APT were SRT = 5 d, G = 152 s −1 and RSR = 10%, SCOD and VFA production were 57.0 mg/L and 21.7 mg/L. Particulate organic matter in sludge was converted into SCOD and VFAs as fermentative bacteria were significantly enriched in APT. Moreover, the APT process was applied in a wastewater treatment plant to solve the problem of insufficient carbon source. The outcomes demonstrated that influent SCOD of biological tank increased by 31.1%, which improved the efficiency of removing nitrogen and phosphorus. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) has long been used to treat different types of organic wastes especially in the developed world. However, organic wastes are still more often considered as a waste instead of a resource in the developing world, which contributes to environmental pollution arising from their disposal. This study has been conducted at Bugolobi Sewage Treatment Plant (BSTP), where two organic wastes, cow manure and brewery sludge were co-digested with primary sludge in different proportions. This study was done in lab-scale reactors at mesophilic temperature and sludge retention time of 20 d. The main objective was to evaluate the biodegradability of primary sludge generated at BSTP, Kampala, Uganda and enhance its ability of biogas production. When the brewery sludge was added to primary STP sludge at all proportions, the biogas production rate increased by a factor of 3. This was significantly (p<0.001) higher than observed gas yield (337±18) mL/(L·d)) in the control treatment containing (only STP sludge). Co-digesting STP sludge with cow manure did not show different results compared to the control treatment. In conclusion, Bugolobi STP sludge is poorly anaerobically degradable with low biogas production but co-digestion with brewery sludge enhanced the biogas production rate, while co-digestion with cow manure was not beneficial. [ABSTRACT FROM AUTHOR]

The effect of thermal pre-treatment on sludge anaerobic digestion (AD) efficiency was studied at different total solids (TS) concentrations (20.0, 30.0 and 40.0 g TS/L) and digestion times (0, 5, 10, 15, 20 and 30 days) for primary, secondary and mixed wastewater sludge. Moreover, sludge pre-treatment, AD and disposal processes were evaluated based on a mass-energy balance and corresponding greenhouse gas (GHG) emissions. Mass balance revealed that the least quantity of digestate was generated by thermal pre-treated secondary sludge at 30.0 g TS/L. The net energy (energy output-energy input) and energy ratio (energy output/energy input) for thermal pre-treated sludge was greater than control in all cases. The reduced GHG emissions of 73.8 × 10 −3 g CO 2 /g of total dry solids were observed for the thermal pre-treated secondary sludge at 30.0 g TS/L. Thermal pre-treatment of sludge is energetically beneficial and required less retention time compared to control. [ABSTRACT FROM AUTHOR]

Background Estrogenic compounds have been detected in the secondary effluents and in the biosolids from conventional wastewater treatment plants, which are not designed for their removal. Furthermore, existing limited studies on anaerobic digestibility of estrogens report conflicting results. The objective of the present work was to determine the fate and anaerobic digestibility of estrogenic compounds in various types of sludge including primary sludge (PS), waste activated sludge (WAS), and anaerobically digested sludge (seed). Methods Estrone (E1) and 17-β estradiol (E2) were chosen as the model estrogenic compounds. Initially batch adsorption was conducted to determine the extent of adsorption and isotherm of E1 on various sludge. Thereafter, batch anaerobic digestion of E1 and E2 was conducted in various sludge using So/X ratio of 4 gCOD/gVSS in 250 ml bottles. The effect of earlier optimized ultrasonication dosage on the anaerobic digestion of E1 and E2 was also characterized. Estrogenicity of the digested samples was determined by the YES assay. Results Most of E1 and E2 was adsorbed on the biosolids and the Freundlich isotherm fitted the experimental data well. No anaerobic digestion of E1 and E2 was found in any of the sludge tested, and the estrogenicity of the sludge measured by YES assay increased during digestion due to the formation of E2 from E1 in a reduced environment. Ultrasonication decreased the initial mass of E1 and E2 by 20% in the sonicated digester as compared to control digester, however, there was no further decrease in E1 and E2 during digestion. Conclusions Most of the estrogenic compounds partitioned onto the solids and remained there during digestion. Ultrasonication pretreatment reduced the estrogen burden for the digester due to advance oxidation, but no further removal of the estrogens occurred in the digester. [ABSTRACT FROM AUTHOR]

Predicting the rheological behaviour of sludge is essential in the design and optimisation of various unit operations of waste water treatment, most notably anaerobic digestion whereby the efficient mixing of sludge feed produces biogas and digested sludge. In this paper, the rheological behaviour of primary sludge (2.8%, 3.7%, 5.5%, 6.8% and 8.2% TS) and secondary sludge (2.8%, 4.0%, 5.0%, 6.5% and 9.2% TS) has been investigated. At low stress, below the yield stress, sludge behaved as a visco-elastic solid, whereby primary sludge yielded abruptly whilst secondary sludge flowed smoothly to steady state. In the steady state, both sludges behaved as shear thinning, yield stress fluids with primary sludge exhibiting highly thixotropic behaviour. The apparent viscosity, yield stress and fluid consistency of both primary and secondary sludge increase with increasing total solids concentration and followed the Herschel-Bulkley model. A master curve was developed based on the dimensionless form of the Herschel-Bulkley model allowing the rheology of primary and secondary sludge at any concentration to be determined. [ABSTRACT FROM AUTHOR]

The investigation provides experimental evidence that the unbiodegradable particulate organics fractions of primary sludge and waste activated sludge calculated from activated sludge models remain essentially unbiodegradable in anaerobic digestion. This was tested by feeding the waste activated sludge (WAS) from three different laboratory activated sludge (AS) systems to three separate anaerobic digesters (AD). Two of the AS systems were Modified Ludzack – Ettinger (MLE) nitrification-denitrification (ND) systems and the third was a membrane University of Cape Town (UCT) ND and enhanced biological P removal system. One of the MLE systems and the UCT system were fed the same real settled wastewater. The other MLE system was fed raw wastewater which was made by adding a measured constant flux (gCOD/d) of macerated primary sludge (PS) to the real settled wastewater. This PS was also fed to a fourth AD and a blend of PS and WAS from settled wastewater MLE system was fed to a fifth AD. The five ADs were each operated at five different sludge ages (10–60d). From the measured performance results of the AS systems, the unbiodegradable particulate organic (UPO) COD fractions of the raw and settled wastewaters, the PS and the WAS from the three AS systems were calculated with AS models. These AS model based UPO fractions of the PS and WAS were compared with the UPO fractions calculated from the performance results of the ADs fed these sludges. For the PS, the UPO fraction calculated from the AS and AD models matched closely, i.e. 0.30 and 0.31. Provided the UPO of heterotrophic (OHO, fE_OHO) and phosphorus accumulating (PAO, fE_PAO) biomass were accepted to be those associated with the death regeneration model of organism “decay”, the UPO of the WAS calculated from the AS and AD models also matched well - if the steady state AS model fE_OHO = 0.20 and fE_PAO = 0.25 values were used, then the UPO fraction of the WAS calculated from the AS models deviated significantly from those calculated with the AD models. Therefore in plant wide wastewater treatment models the characterization of PS and WAS as defined by the AS models can be applied without modification in AD models. The observed rate limiting hydrolysis/acidogenesis rates of the sludges are listed. [ABSTRACT FROM AUTHOR]

BACKGROUND Management of the sludge generated in the wastewater treatment plants accounts for more than 50% of their operational costs. To minimise these costs, technologies capable of reducing the production of sludge in the plant need to be developed, such as aerobic granular systems. The aggregation state of aerobic granular sludge ( AGS) could be a limiting factor for its further anaerobic digestion. Therefore in this work the feasibility of anaerobic digestion of AGS has been studied under three conditions: (1) raw AGS, (2) thermal pre-treated AGS and (3) a mixture of thermal pre-treated AGS with primary sludge. RESULTS The values obtained for anaerobic biodegradability and reduction of solids in the case of raw AGS were 44% and 32%, respectively. Thermal pre-treatment of AGS at 133 °C enhanced the anaerobic digester performance, in terms of solids reduction, by approximately 47%. The mixture of thermal pre-treated AGS with primary sludge provided better results for solids removal than in the case with only thermal pre-treated AGS. CONCLUSION Anaerobic digestion of AGS has a similar performance as that reported for waste activated sludge, which indicates that the aggregation of the biomass into granules does not seem to limit the anaerobic process. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery. [ABSTRACT FROM AUTHOR]

The objective of this study was to compare some basic characteristics of sludge from fine mesh sieves (sieve sludge) with sludge from primary clarifiers (primary sludge) regarding their energy potential with a focus on anaerobic digestion and/or incineration. Nineteen samples of sludge from fine mesh sieve plants (most of them without fine screens and grit chambers as pre-treatment) and 10 samples of primary sludge were analysed for the content of dry solids (DS), volatile solids (VS), chemical oxygen demand (COD), calorific value and methane potential. The results demonstrated that the sieve sludges have significantly higher VS content and higher methane potential than primary sludges, clearly indicating an increased sludge energy potential if fine mesh sieves are used for primary treatment instead of primary clarifiers at wastewater treatment plants with anaerobic digesters. If the sludges from primary treatment are to be incinerated or used as fuel in cement kilns, there is no significant difference in energy potential (given as calorific values) for the two types of primary treatment. [ABSTRACT FROM AUTHOR]

The sludge production from medium- and small-scale wastewater treatment plants in the Three Gorges Reservoir Region is low and non-stable; especially, the organic content in this sludge is low (near 40% of VS/TS). An integrated thickening and digestion (ISTD) reactor was developed to treat this low-organic excess sludge. After a flow test and start-up experiment of the reactor, a running experiment was used to investigate the excess sludge treatment efficiency under five different excess sludge inflows: 200, 300, 400, 500 and 400 L/d (a mixture of excess sludge and primary sludge in a volume ratio of 9:1). This trial was carried out in the wastewater treatment plant in Chongqing, which covers 80% of the Three Gorges Reservoir Region, under the following conditions: (1) sludge was heated to 38–40 °C using an electrical heater to maintain anaerobic mesophilic digestion; (2) the biogas produced was recirculated to mix raw sludge with anaerobic sludge in the reactor under the flow rate of 12.5 L/min. There were three main results. Firstly, the flow pattern of the inner reactor was almost completely mixed under the air flow of 12.0 L/min using clear water. Secondly, under all the different sludge inflows, the water content in the outlet sludge was below 93%. Thirdly, the organic content in the outlet sludge was decreased from 37% to 30% and from 24% to 20%, whose removal ratio was in relation to the organic content of the inlet sludge. The excess sludge treatment capacity of the ISTD reactor was according to the organic content in the excess sludge. [ABSTRACT FROM PUBLISHER]

Abstract: The use of different carbon sources (ethanol, acid-fermented primary sludge centrate, acid-fermented secondary sludge centrate, glycerol and landfill leachate) in heterotrophic denitrification from nitrite (denitritation) was studied in a sequencing batch reactor, operated without pH control. Complete denitritation of a high-strength nitrite wastewater was achieved using these organic carbon sources with the exception of fermented secondary sludge centrate. Loading rates around 0.2gNL−1 d−1 were obtained for glycerol, landfill leachate and ethanol after a short start-up period of 20 days. The maximum specific nitrite removal rate of 0.25gNg−1 VSSd−1 was achieved for glycerol, while values between 0.13 and 0.17gNg−1 VSSd−1 were obtained using ethanol, landfill leachate and fermented primary sludge centrate. The COD/N ratio consumed varied between 3.0 for ethanol and 8.8 for landfill leachate. The denitritation rates and the required COD/N ratio for each carbon source are reported for the first time – they can be used for the scale-up of the denitritation process. [Copyright &y& Elsevier]

Generation of solid waste is inherent to manufacture of leather from skin and hide. Solid wastes generated at various unit operations of the tanning process considerably vary in quantity and composition. Fleshing is a type of animal tissue waste generated during the preparatory leather processing stage in relatively larger quantities as compared to other types of solid waste in the tanning industry. Fleshing mainly contains fat and protein and residual chemicals such as lime and sulphide used in the 'unhairing' process of beam house operation. Another type of solid waste in tanning industry which requires safe disposal is the primary sludge from tannery wastewater treatment plant. This study shows that both fleshing and primary sludge contains a significant quantity of volatile solids amenable for biodegradation. Different proportions of waste fleshing and primary sludge were subjected to anaerobic digestion. The studies were carried out in a laboratory scale reactor with an aim of developing an appropriate technology for recovery of bioenergy from the waste and subsequently ensure their safe disposal. Volatile solid destruction between 41 and 52%, specific gas production between 0.419 and 0.635 l/g volatile solids feed and methane yield between 71 and 77% were achieved. Further, the biomethanation potential of animal fleshing and substrate specific kinetics of the reaction process were also examined. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic digestion of brewery wastewater solids in the form of primary sludge was investigated for its potential as a source of energy (methane). We operated a low-rate (hydraulic retention time (HRT)=solids retention time (SRT)) continuously stirred anaerobic digester (CSAD) and a high-rate (SRT>HRT) anaerobic sequencing batch reactor (ASBR) in parallel for 250days. We found that high-rate anaerobic digestion was beneficial for solids-rich waste flows even during a long-term operating period that included a shock load of nonbiodegradable total solids. The ASBR biomass achieved a higher specific methanogenic activity compared to the CSAD biomass (0.257±0.043 vs. 0.088±0.008g CH4-CODg−1 VSSd−1), which aided in stability during the shock load with total solids. The methane yield for the ASBR was 40–34% higher than for the CSAD (0.306 vs. 0.219l CH4 gVS−1 fed for days 1–183 and 0.174 vs. 0.130l CH4 gVS−1 fed for days 184–250, respectively). Finally, we operated an ASBR for an additional 295days to evaluate the effect of temperature variation on system stability. A stable performance was achieved between the operating temperatures of 22–41°C. [Copyright &y& Elsevier]

Co-digestion of the organic fraction of municipal solid waste (OFMSW) and sewage sludge may be an attractive alternative for sustainable management of two separate waste streams produced in large amounts in all countries. This study evaluates calculation- based results of an anaerobic co-digestion process for primary sludge (PS) together with the OFMSW. The calculations were carried out for the anaerobic digester of Kayseri municipal wastewater treatment plant (in Turkey) presently digesting only PS. Two alternatives were proposed using different solid waste contents in co-digesters. For achieving the optimal solids content, some treated wastewater should be recycled to the inlet of the digesters. The municipal solid waste collection method characterized as mechanically sorted (MS-OFMSW; Option 1) is evaluated as well as a source sorted (SS-OFMSW) alternative (Option 2). Utilizing the energy produced by the existing sludge digester, only 30% of the internal energy demand at the wastewater treatment plant can be covered. The aim of this study is to evaluate how energy production would be increased by co-digestion of OFMSW and PS. The best operational condition considering organic loading rate, hydraulic retention time and energy generation could be attained at 10% digester solids content for both options. According to Option 1, almost 77% of the energy demand could be covered by co-digestion of MS-OFMSW and PS. Results indicated that almost 100% energy coverage can be obtained when co-digestion (Option 2) was performed according to SS-OFMSW and PS. [ABSTRACT FROM AUTHOR]

Abstract: Sludge drying reed beds (SDRBs) are a combination of traditional sludge drying beds and constructed wetlands. Their main advantages include low investment, infrequent biosolids removal (of the order of years), dewatering and mineralization of biosolids, minimization of biosolid volume, simplicity and economy, and production of a beneficial, well-composted side product. A constructed wetland facility is used to treat the sewage from the municipality of Nea Madytos, Thessaloniki Province, North Greece. The primarily produced biosolids in the Imhoff tank of this facility are treated with a vertical flow SDRB. The performance and dewatering efficiency of this system was monitored for 1year. Over the 12years of operation of the treatment plant, 7884m3 of biosolids from the Imhoff tank were transferred to the SDRBs. Until today, no biosolids were removed, and the level of the dewatered sludge on the bed is built to about 20cm, with a volume of residue sludge of 28m3. This corresponds to a biosolid reduction of 99.64%. At the end of the examination period the TS (VS) content varied from 55% (40%) in the top layer to 65% (35%) in the bottom layer. The heavy metal concentration meets the European Union standards for heavy metals in case of agricultural disposal of the treated sludge. [Copyright &y& Elsevier]

Laboratory experiments have been utilised as a tool to determine the possible yield of soluble COD and VFAs from settled influent and preprecipitated sludge at Klagshamn wastewater treatment plant and to determine the degradability of the organic matter. The release of ammonium and orthophosphate from the hydrolysed sludge has been estimated. It is possible to produce soluble organic matter of good quality from settled influent and preprecipitated sludge at Klagshamn WWTP. Denitrification rates of 3.1mg NO3ZN/(g VSS x h) were found for the hydrolysate in laboratory tests. Owing to the low phosphate concentrations in the hydrolysate from preprecipitated sludge, it shows a potential for postdenitrification despite stringent phosphorus outlet demands. Calculations based on data gained from the laboratory experiments show that about 50% of the external carbon source used today can be saved with minor changes in the plant operation except that the hydrolysis has to be established. Based on these findings, full-scale experiments with internal hydrolysis in the primary clarifiers were scheduled in one of the two lines at Klagshamn WWTP for the summer of 2007. [ABSTRACT FROM AUTHOR]

An efficient biological treatment to treat reject water from anaerobic digestion of wastewater sludge is the SHARON denitrification process, which takes place in a chemostat reactor, where aerobic/anoxic periods are alternated under specific hydraulic retention time (HRT) and temperature conditions that favor ammonium oxidizers growth and ensure the total washout of nitrite oxidizers, achieving the biological nitrogen removal over nitrite. An optimized performance of this process to treat Spanish reject water was obtained using methanol and working at an HRT of 2 days, 33°C, and cycle length of 2 hours. Supernatant of hydrolyzed primary sludge was tested to denitrify. Because biochemical oxygen demand was not extremely high in the primary sludge, the fluid dynamics of the system were changed, with respect to the strategy with methanol, but maintaining the reject water influent flowrate. The use of hydrolyzed primary sludge improved the process efficiency, because the alkalinity present in the primary sludge buffered the process until an optimum pH range. [ABSTRACT FROM AUTHOR]

Abstract: Biosolids pellets produced from anaerobically digested municipal wastewater sludge by drying to greater than 90% total solids at 110–115°C for at least 75min, were tested for their suitability as an inoculum source for fermentative hydrogen production. The hydrogen recoveries (mg gaseous H2 produced as COD/mg added substrate COD) for glucose-fed batch systems were equal, 20.2–21.5%, between biosolids pellets and boiled anaerobic digester sludge as inoculum sources. Hydrogen recoveries from primary sludge were 2.4% and 3.5% using biosolids pellets and boiled sludge, respectively, and only 0.2% and 0.8% for municipal wastewater. Biosolids pellets should be a practical inoculum source for fermentative hydrogen reactors, although the effectiveness will depend on the wastewater treated. [Copyright &y& Elsevier]

Anaerobic digestion is an appropriate technique for the treatment of sludge before final disposal and it is employed worldwide as the oldest and most important process for sludge stabilization. In general, mesophilic anaerobic digestion of sewage sludge is more widely used compared to thermophilic digestion. Furthermore, thermal pre-treatment is suitable for the improvement of stabilization, enhancement of dewatering of the sludge, reduction of the numbers of pathogens and could be realized at relatively low cost especially at low temperatures. The present study investigates (a) the differences between mesophilic and thermophilic anaerobic digestion of sludge and (b) the effect of the pre-treatment at 70°C on mesophilic and thermophilic anaerobic digestion of primary and secondary sludge. The pre-treatment step showed very positive effect on the methane potential and production rate upon subsequent thermophilic digestion of primary sludge. The methane production rate was mostly influenced by the pre-treatment of secondary sludge followed by mesophilic and thermophilic digestion whereas the methane potential only was positively influenced when mesophilic digestion followed. Our results suggest that the selection of the pre-treatment duration as well as the temperature of the subsequent anaerobic step for sludge stabilization should depend on the ratio of primary to secondary sludge. [Copyright &y& Elsevier]

Improving the treatment efficiency of sludge in Alexandria, Egypt, was studied to improve the primary and secondary sludge treatment efficiency, different doses ranging from 0.25 to 6 kGy of ionizing radiation were proposed and evaluated. The scope of This study is to assess the radiation-based treatment efficiency from physical, chemical, and biological perspectives and to compare between the conventional treatment method and the radiation-based treatment technology. To evaluate the performance of each treatment system, pH, oil and greases concentrations, total solid concentrations, BOD concentrations, COD concentrations, parasites, and microorganisms were assessed in the primary and secondary samples at different radiation doses (from 0.25 to 6 KGy), and in the conventionally treated samples. Irradiation by gamma radiation with a dose ranging from 0.25 to 6 kGy was efficient in reducing some of the physical contaminants. Oil & greases, Total Solids, BOD, COD concentrations were reduced significantly (p < 0.001) in a dose-dependent manner. Either primary or secondary sludge samples, total solid reduced significantly to about one-third of control concentration at six kGy. Six kGy able to reduce the BOD and COD concentrations in the primary sludge samples to that of the treated (after sludge dewatering) samples or less respectively and saved the secondary treatment stage. In primary and secondary sludge samples culture, E. coli , Staphylococcus aureus , and Vibrio spp were isolated as heavy growth on different culture media in the samples before radiation. After exposure to increasing doses of radiation, the number of isolated organisms decreased, however, the growth of Proteus, Acinetobacter, and vipro organisms was detected but in small numbers. No growth of any organism was noted at 5 kGy. On the other hand, in the secondary sludge samples, Proteus was isolated as heavy growth before radiation and After exposure to increasing doses of radiation, Moraxella spp. organisms were detected but in small numbers. By increasing the radiation doses, the free-living ciliates were decreased in the primary and secondary sludge samples. The free-living ciliates disappeared completely at 3 kGy. In the primary and secondary sludge samples, free-living ciliates reduction efficiency at 0.25 kGy was equivalent to the conventional treatment methods. So, we can conclude that radiation technology using Gamma rays at a dose higher than 5 kGy with a dose rate of 1.095 kGy/h is an effective technology for domestic and industrial waste sludge treatment from the environmental perspective and an experimental pilot plant study is required to optimize the cost of wastewater treatment through the use of irradiation technology. Recommendations: ❖ Either in primary or secondary sludge samples, the concentration of oil & greases reduced significantly (p < 0.001) in a dose dependent manner, that leads us to investigate later a higher radiation doses which might reduce the concentration of oil & greases to the level of the treated samples. ❖ An experimental pilot plant study is required to optimize the cost of wastewater treatment using irradiation technology. ❖ Study the other perspectives like economy and/or social. ❖ Study the effect of radiation on surfactants, nitrogen and phosphorus ingredients, heavy metal ions and other sludge components. [ABSTRACT FROM AUTHOR]

Municipal wastewater treatment suffers the general problems of poor denitrification and low phosphorus removal caused by insufficient carbon sources. Thus, a baffled reactor was developed to provide additional carbon by hydrolysis and acidification of the primary sludge in the A²/O process in order to treat low C/N ratio wastewater. The effects on denitrification and phosphorus removal were evaluated. The results showed that CTN, CTP, CCOD, and ...-N in the effluent were concentrated at 17, 0.5, 30, and 1.6mg/L, respectively, while the removal efficiencies rose to 69.6, 92.5, 88, and 96.7%, respectively, while dosing acidified primary sedimentation sludge. Compared with control groups that did not receive acidification liquid, CTN, CTP, and ...-N of the effluent were decreased by 8.7, 1.3, and 0.7mg/L, respectively, and the removal efficiencies were correspondingly increased by 15.6, 22.5, and 1.7%, respectively. These data demonstrated that adding acidified primary sludge effectively improved the removal of nitrogen and phosphorus nutrients. [ABSTRACT FROM AUTHOR]

To treat household wastewater, a sequence of 'primary decantation-trickling filter percolation' was applied in a lab-scale designed treatment system. Poly-electrolyte was used as coagulant to enhance the primary treatment and charcoal was used as carrier material in the trickling filters. Oxygen was supplied to the trickling filters by means of natural ventilation. In the lab-scale system, the enhanced primarystage removed more than 91% of the suspended solids (SS), and 79% ofthe total chemical oxygen demand (CODt). The subsequent trickling filtration brought a complete nitrification to the wastewaters at a volumetric loading rate (Bv) of 0.7-1.0 g CODt L-1 d-1. On average, the concentrations of the CODt and SS in the final effluents were about 55 and 15 mg L-1 respectively. With respect to phosphate, physico-chemical removal was the dominant process. About 46-62% of total P was removed from the tested wastewaters. The integrated treatment system also achieved a fair degree of hygienisation. The numbers of total coliforms, fecal coliforms and fecal streptococci were decreased by 2-4 log units. The sludge production of the entire treatment system was about 1.7% (v/v) of the treated wastewater. Only primary sludge was produced; secondary sludge produced in the trickling filters was negligible. The cost savings in terms of minimization of sludge production and aeration energy are estimated to be substantial (i.e. some 50%) relative to a conventional activated sludge system. [ABSTRACT FROM AUTHOR]