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The work concerns the study of the hydrochar from digestate and hydrochar co-compost characterization as amendments. The processes for hydrochar and co-compost production were described in Part 1 of this work (Scrinzi et al., 2022). The amendment properties of hydrochar (produced at 180-200-220 °C for 3 h) and co-composts (25%, 50%, and 75% hydrochar percentage of digestate substitution) were assessed by phytotoxicity, plant growth bioassay, and soil effect. Different seeds species (Lepidium sativum, Cucumis sativus, and Sorghum bicolor sp.) were dosed at increased concentrations using both wet raw amendments and their water extracts. The chemical characterization showed phytotoxic compounds content depending on both the initial feedstock (digestate) and the HTC process; at the same time, the analysis highlighted the reduction of these compounds by composting (organic acid, polyphenols, salt concentration). The dose-response was analyzed by the Cedergreen-Streibig-Ritz model and the half-maximal effective concentration (EC50) was calculated based on this equation. The soil properties and GHG emissions measurements (CH

Sewage sludge is the by-product of wastewater treatment processes. Its reuse is central to a circular economy approach and offers a sustainable alternative to its disposal. Treated sludge contains a wide range of nutrients (mainly nitrogen, phosphorus, and potassium), which favor its sustainable employment for agricultural purposes (land-spreading, compost production) and environmental requalification interventions (forestry, silviculture, land reclamation and revegetation). However, if not properly treated, sewage sludge can contain various contaminants such as heavy metals, organic pollutants, pathogens, and other emerging contaminants, which pose a threat for crops production and human health. Hydrodynamic cavitation (HC) is an eco-friendly and cost-efficient pretreatment that can enhance sewage sludge stabilization in both anaerobic and aerobic digestion units, thereby making safe its management and disposal. In this study, HC was used for the gradual disintegration of activated sludge (reaching a maximum disintegration degree (DDPCOD) of 19.2% after 8 h of treatment), and the solubilization of the dissolved organic matter (increasing the Soluble Chemical Oxygen Demand (SCOD) from 244 to 4,578 mg L−1 after 8 h of treatment). Then, both dynamic light scattering analysis and stereoscopic microscope observations proved that HC can also lead to a size reduction of sludge suspended particles. In addition to evaluate the HC treatment efficiency, in this work was also provided a brief discussion on the possible procedures to be followed for the safe and efficient sewage sludge disposal on land after it has been HC-treated.

In recent years, sewage sludge (SS) and bio-waste management have attracted increasing environmental attention. In this study, hydrothermal carbonization (HTC) technology is investigated in the framework of a co-treatment of sewage sludge digestate (SSD) and an organic fraction of municipal solid waste (OW). The proposed configuration integrates HTC with anaerobic digestion (AD) in an inter-stage configuration (AD1 + HTC + AD2). The effects of different percentages of OW added to SSD in the HTC treatment are evaluated in terms of characteristics and methane yield of the produced HTC liquor (HTCL) and HTC slurry (i.e., the mixture hydrochar-HTCL), as well as dewaterability of the HTC slurry. Results show that, with the increase in the percentage of OW in the OW-SSD mixture fed to the HTC process, production of biogas and biomethane of both HTC slurry and HTCL increases. The highest biogas production is achieved when a mixture consisting of half SSD and half OW is used, reaching 160 ± 10 and 240 ± 15 mL biogas g−1 CODadded, respectively, for HTCL and HTC slurry. Furthermore, sludge dewaterability is significantly improved by the combined AD1-HTC-AD2 process. Finally, an energy assessment allows estimating that the co-treatment of OW with SSD in HTC can cover up to 100% of the energy consumption of the system.

This study aimed at modelling the performance of a novel MBBR configuration, named A/O-MBBR, comprised of a pre-anoxic reactor, with an HRT of 4.5 h, coupled with an intermittent anoxic/aerobic MBBR (HRT = 6.8 h). The lab-scale system was fed with municipal wastewater with an average influent Total Ammonia Nitrogen (TAN) and total COD (TCOD) concentrations of 46 mg of TAN-N L-1 and 310 mg TCOD L-1. During the whole experimental period, TAN removal efficiency was always higher than 96%; denitrification was also very effective, achieving nitrate and nitrite concentrations in the effluent both lower than 5 mg NOx-N L-1 on average. Moreover, TCOD average removal efficiency was equal to 85%. Modelling was performed to investigate the nitrification efficacy enhancement; to this aim, a biofilm model was developed, adopting the equations for mixed-culture biofilms and the Activated Model Sludge n°1 (ASM1) for the biological processes rates. The model allowed to determine the maximum uptake rate for autotrophic growth (μA was 2.5 d-1) and the semisaturation constant (KOA was 0.2 mg O2 L-1), suggesting that the nitrification process was 3-fold faster than average and very effective at low oxygen concentrations. The model estimated that about 85% of TAN was removed by the biofilm and only the remaining part by suspended biomass in the bulk liquid. Finally, it was assessed that the A/O-MBBR configuration allowed for a 45-60% savings of the energy requirement compared to a Benchmark WWTP layout.

This study evaluates the effects of thermal hydrolysis (TH) pretreatment on anaerobic digestion (AD), through results obtained by biochemical methane potential (BMP) tests under mesophilic conditions (35 °C). Thickened sludge from a wastewater treatment plant (WWTP) was thermally treated under two different temperatures (150 and 170 °C) and reaction times (30 and 60 min). Results show a significant increase in soluble COD, compared with the untreated sludge, when sludge was treated at 170 °C for 60 min. Moreover, the following BMP tests point out that TH pretreatment of sludge accelerated the AD rate and increased the biogas yield contributing to an increase in methane production, ranging between 17 and 24% compared with the raw sludge. Furthermore, the hydrolysis constant was estimated and methane production and degree of disintegration of the TH pretreated sludge were correlated, in order to deep the knowledge on the hydrolysis as the AD rate-limiting step. Further, the combined effects of TH pretreatment and AD on sludge show a reduction of total and volatile solids up to 19% and 24%, respectively.

Fenton is one of the advanced oxidation processes that can oxide organic compounds efficiently increasing the dewaterability of sludge. This study reports the optimisation of two reagents, Fe2+ and...

The present work aims to analyze the valorization of blood (Category 3 animal by-products). In this study, for the first time, blood serum water, obtained after a sterilization process and a solid/liquid separation unit, has been utilized as energy rich input material for anaerobic digestion. The performance of an up-flow anaerobic filter (UAF) for treating bovine blood serum water under mesophilic conditions was investigated. The reactor was loaded up to an organic loading rate of 2.5 kg m−3 d−1 of total COD, achieving total and soluble COD removal efficiencies of 90% and 92%, respectively. A maximum biogas yield of 0.56 m3 kg−1 of removed total COD was measured. According to the modified Stover-Kincannon kinetic model, maximum removal rate constant, Umax, and saturation value constant, KB, values were estimated as 18.8 g L−1 d−1 and 18.5 g L−1 d−1 for blood serum water, respectively. As the model gave high correlation coefficients (R2 = 97%), it could be used in both designing and predicting the behaviour of the UAF.

In order to reduce the investment costs of the anaerobic side-stream reactor (ASSR) process coupled with an activated sludge system and promote the full scale application, the impact of 1 d anaerobic solid retention time (SRTASSR) and 100% interchange ratio (IR) has been investigated on sludge reduction, carbon and nutrient removal efficiency and microbial community, in a sequencing batch reactor (SBR)-ASSR system. The SBR-ASSR achieved good removal efficiencies in COD (91.5 ± 3.4%), ammonium nitrogen (98.8 ± 0.5%), total nitrogen (87.9 ± 4.9%) and phosphate (92.8 ± 6.7). The sludge yield of the system was 0.1648 g TSS g−1COD; 54% lower compared to a conventional activated sludge (CAS) system. Real time quantitative polymerase chain reaction (q-PCR) showed an abundance of hydrolyzing and fermentative bacteria. Comparison at class and genus level confirmed an abundance of anaerobic hydrolyzing and fermentative bacteria, denitrifying bacteria able to simultaneous perform nitrogen and phosphate removal and phosphate accumulating organisms.

An increasing number of industrial plants integrate the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) with a subsequent composting phase. To improve the plant productivity, a fraction of OFMSW digestate can be converted into a carbonaceous material, called hydrocar (HC), through Hydrothermal Carbonization (HTC), and then composted together with the OFMSW digestate itself, to produce “hydrochar co-compost”. The aim of this paper is to present the design and assembly of batch bioreactors, built in-house to investigate the co-composting process of OFMSW digestate and its HC, and to provide some preliminary results. The OFMSW digestate from an industrial plant was carbonized at 200 °C for 3 h in a 2 L HTC reactor, to produce wet HC after filtration. The ratio of OFMSW digestate and green waste (1:1) used as bulking medium was reproduced in four bioreactors with an increasing percentage of HC substituting the OFMSW digestate (0, 25, 50, 75%). The bioreactors managed to effectively compost the solid wet biomasses in a wet environment with temperature and oxygen control, while measuring online the oxygen consumption and thus the dynamic respirometric index (DRI). The DRI24,max measured with AIR-nl solid respirometer (standardized offline measurement) started from values above 800 mg O2 kgVS−1 h−1 before composting and dropped at the end of the process to values in the range 124–340 mg O2 kgVS−1 h−1 for the four mixes, well below the recommended limit of 500 mg O2 kgVS−1 h−1 for high-quality compost stability. These offline DRI values were confirmed by the online DRI measurements. This research is part of the international C2Land Project funded by the European Institute of Innovation and Technology Climate Knowledge and Innovation Community (EIT Climate-KIC), which is greatly acknowledged.

Mature landfill leachates are characterized by high levels of ammoniacal nitrogen which must be reduced for discharge in the sewer system and further treatment in municipal wastewater treatment plants. The use of anammox-based processes can allow for an efficient treatment of ammonium-rich leachates. In this work, two real scale sequencing batch reactors (SBRs), designed to initially perform partial nitritation/anammox (PN/A) and simultaneous partial nitrification and denitrification (SPND) for the treatment of ammonium-rich urban landfill leachate, were modelled using BioWin 6.0 in order to enable plant-wide modelling and optimizing. The constructed models were calibrated and validated using data from long- and short-term (one cycle) SBR operation and fit well to the main physical-chemical parameters (i.e., ammonium, nitrite and nitrate concentrations) measured during short-term (one cycle) operations. Despite the different strategies in terms of dissolved oxygen (DO) concentrations and aeration and mixing patterns applied for SBR operation, the models allowed for understanding that in both reactors the PN/A process was shown as the main contributor to nitrogen removal when the availability of organic carbon was low. Indeed, in both SBRs, the activity of nitrite oxidizing bacteria was inhibited due to high levels of free ammonia, whereas anammox bacteria were active due to the simultaneous presence of ammonium and nitrite and their ability to recover from DO inhibition. Increasing the external carbon addition, a prompt decrease of the anammox biomass was observed, with SPND becoming the main nitrogen removal mechanism. Models were also applied to estimate the production rates of nitrous oxide by aerobic ammonia oxidizing bacteria and heterotrophic denitrifiers. The models were found to be a robust tool for understanding the effects of different operating conditions (i.e, temperature, cycle phases, DO concentration, external carbon addition) on the nitrogen removal performances of the two reactors, assessing the contribution of the different bacterial groups involved.

The best available technique (BAT) for managing the organic fraction of municipal solid waste (OFMSW) is represented by anaerobic digestion (AD) and subsequent composting. This research explored a new industrial model in the framework of the C2Land international project, with the insertion of hydrothermal carbonization (HTC) as a post-treatment for OFMSW digestate. The reaction was set for 3 h at three different temperatures (180 ÷ 220 °C); the wet solid hydrochar obtained after filtration was then co-composted with greenery waste as a bulking agent and untreated OFMSW digestate in four different proportions in bench-scale bioreactors. The hydrochars and the hydrochar co-composts were suitable for agro-industrial applications, while the HTC liquors were tested in biochemical methane potential (BMP) for internal recirculation to AD. The scenarios proposed can be beneficial for plant enhancement and increased biogas production. This study reports results connected to the production phase. Mass balances confirmed that, during HTC, phosphorus precipitated into the solid products, organic nitrogen partially mineralized into ammonium, and oxidizable organic matter solubilized. The selected hydrochar obtained at 200 °C had mean (dry) solid, liquid, and gaseous yields equal to 77, 20, and 3 %

The increased quantities of manure being generated by livestock and their extensive agronomic use have raised concerns around run-off impacting soil and groundwater quality. Manure contains valuable nutrients (especially phosphorus) that are critical to agriculture, but when directly land-applied the run-off of such nutrients contributes to eutrophication of waterways. This study investigates the hydrothermal carbonization of cow manure at two industrially feasible process extremes: 190 °C, 1 h and 230 °C, 3 h, to concentrate and then recover phosphorus from the solid hydrochar via acid leaching and precipitation. Up to 98 wt% of phosphorus initially present in the hydrochar (88% in the raw manure) can be recovered, with the dominant crystalline species being hydroxyapatite. Acid leached hydrochars were subsequently pyrolyzed at 600 °C for 30 min, and then evaluated as adsorbent materials for water remediation by using methylene blue as a model adsorbate. Although pyrolyzed hydrochars have surface areas an order of magnitude higher (160-236 m

The present study addresses the coupling of hydrothermal carbonization (HTC) with anaerobic digestion (AD) in wastewater treatment plants. The improvement in biomethane production due to the recycling back to the anaerobic digester of HTC liquor and hydrochar generated from digested sludge is investigated and proved. Mixtures of different compositions of HTC liquor and hydrochar, as well as individual substrates, were tested. The biomethane yield reached 102 ± 3 mL CH4 g−1 COD when the HTC liquor was cycled back to the AD and treated together with primary and secondary sludge. Thus, the biomethane production was almost doubled compared to that of the AD of primary and secondary sludge (55 ± 20 mL CH4 g−1 COD). The benefit is even more significant when both the HTC liquor and the hydrochar were fed to the AD of primary and secondary sludge. The biomethane yield increased up to 187 ± 18 mL CH4 g−1 COD when 45% of hydrochar, with respect to the total feedstock, was added. These results highlight the improvement that the HTC process can bring to AD, enhancing biomethane production and promoting a sustainable solution for the treatment of the HTC liquor and possibly the hydrochar itself.

Hydrothermal carbonization (HTC) technology is addressed in the framework of sewage digestate management. HTC converts digestate into a stabilized and sterilized solid (the hydrochar) and a liquor (HTCL) rich in organic carbon. This study aims to optimize the HTC operating parameters, namely the treatment time, in terms of hydrochar production, HTC slurry dewaterability, HTCL bio-methane yields in anaerobic digestion (AD), and process energy consumption. Digestate slurry was processed through HTC at different treatment times (0.5, 1, 2 and 3 h) at 190 °C, and the dewaterability of the treated slurries was addressed through capillary suction time and centrifuge lab-testing. In addition, biochemical methane potential (BMP) tests were conducted for HTCL under mesophilic conditions. Results show that by increasing the HTC treatment time the dewaterability was further improved, ammonium concentration in HTCL increased, and methane potential of HTCL decreased. 0.5 h HTCL had the highest bio-methane potential of 142 ± 3 mL CH4/g COD yet the treatment time was not sufficient for improving the slurry's dewaterability. HTC treatment time of 1 h at 190 °C was identified as the optimum trade-off for improved dewaterability and utilisation of HTCL for biogas production. 1 h HTCL bio-methane potential can cover around 25% of the HTC and AD thermal and electrical energy needs without considering the eventual use of the hydrochar as a biofuel.

Engineered microalgal-bacteria consortia are an attractive solution towards a low-cost and sustainable wastewater treatment that does not rely on artificial mechanical aeration. In the research conducted for this study, a bench-scale photo-sequencing-batch reactor (PSBR) was operated without external aeration. A spontaneous consortium of microalgae and bacteria was developed in the PSBR at a concentration of 0.8–1.7 g TSS/L. The PSBR ensured removal efficiency of 85 ± 8% for chemical oxygen demand (COD) and 98 ± 2% for total Kjeldahl nitrogen (TKN). Nitrogen balance revealed that the main mechanisms for TKN removal was autotrophic nitrification, while N assimilation and denitrification accounted for 4% and 56%, respectively. The development of dense microalgae–bacteria bioflocs resulted in good settleability with average effluent concentration of 16 mgTSS/L. The ammonium removal rate was 2.9 mgN L−1 h−1, which corresponded to 2.4 mgN gTSS−1 h−1. Although this specific ammonium removal rate is similar to activated sludge, the volumetric rate is lower due to the limited total suspended solids (TSS) concentration (three times less than activated sludge). Therefore, the PSBR footprint appears less competitive than activated sludge. However, ammonium was completely removed without artificial aeration, resulting in a very cost-effective process. Only 50% of phosphorus was removed, suggesting that further research on P uptake is needed.

In the treatment of real municipal wastewater with photo-sequencing batch reactors (PSBR), operating strategies able to achieve high levels of pollutant removal, but reduce the hydraulic retention time (HRT), are imperative for making microalgae-bacteria consortia more competitive than conventional activated sludge systems. In regard to real-time monitoring, on-line probes like Dissolved Oxygen (DO), pH and oxidation–reduction potential (ORP) are cheap and reliable, but their exploitation has been largely overlooked in PSBRs. This paper proposes the use of DO, pH and ORP profiles to reveal the evolution of wastewater treatment in a PSBR treating real municipal wastewater with a mixed consortium of microalgae and bacteria. The PSBR ensured removal efficiency of 87 ± 5% for COD and 98 ± 2% for TKN without external aeration; indeed, photosynthesis was the only driver of the oxygen production. Considering the combined effects of photosynthetic oxygenation and microbial oxygen consumption, some practical information was gathered to understand the complex profiles of the on-line parameters. During dark and light phases, Zero-DO values, DO and pH raises, and their relative peaks were discussed to evaluate correctly the conclusion of the wastewater treatment and therefore to adjust the duration of the PSBR cycle. In particular: (1) two simultaneous “characteristic points”, “Ammonia valley” (pH profile) and “DO breakpoint” (DO profile), detected univocally the complete ammonium removal; (2) the absolute peaks of DO, pH and ORP at maximum irradiance revealed that wastewater treatment was complete and the cycle could be concluded. In this way, these characteristic points were exploited for the optimization of the PSBR cycle, which was concluded after 15–26 h, reducing the HRT by more than 45%.

The optimization of total nitrogen removal from municipal wastewater was investigated in a laboratory-scale photo-sequencing batch reactor (PSBR) operated with a mixed microalgal–bacterial consortium spontaneously acclimatized to real wastewater. No external aeration was provided in the PSBR to reduce energy consumption: oxygen was only supplied by the microalgal photosynthesis. The enhancement of total nitrogen removal was achieved through: (1) feeding of wastewater in the dark phase to provide readily biodegradable COD when oxygen was not produced, promoting denitrification; (2) intermittent use of the mixer to favor simultaneous nitrification–denitrification inside the dense flocs and to achieve 41% energy saving with respect to continuous mixing. Efficient COD removal (86 ± 2%) was observed, obtaining average effluent concentrations of 37 mg/L and 22 mg/L of total COD and soluble COD, respectively. TKN removal was 97 ± 3%, with an average effluent concentration of 0.5 ± 0.7 mg NH4+-N/L. Assimilation of nitrogen by heterotrophic bacteria accounted only for 20% of TKN removal, whilst the major part of TKN was nitrified. In particular, the nitrification rate was 1.9 mgN L−1 h−1 (specific rate 2.4 mgN gTSS−1 h−1), measured with dissolved oxygen near zero, when the oxygen demand was higher than the oxygen produced by photosynthesis. Total nitrogen of 6.3 ± 4.4 mgN/L was measured in the effluent after PSBR optimization.

Several automatic strategies for aeration control have been investigated so far to favor a significant decrement of energy consumptions in biological processes in wastewater treatment plants (WWTPs). Above all, the intermittent aeration process has demonstrated to have several advantages. This work reports the results of a case study made in a small municipal WWTP where an intermittent aeration control strategy based on the online measurement of real-time nitrogen forms has been implemented to optimize the nitrogen removal and the energy consumption in an activated process. High organic removal efficiency was achieved during the whole experimental period. Results indicated that nitrogen removal efficiency has been improved, especially during winter months, by the control strategy adopted that helped to determine the perfect length for the nitrification and denitrification phases. The intermittent aeration process increased the activity of the biomass, further selecting phosphate-accumulating bacteria and improving the growth of bacteria able to internally store carbon source. Excellent effects were achieved on energy and chemical consumption, with a reduction of about 15% and 23%, respectively. Finally, a 12% reduction of sludge production was also detected.

This study investigates the suitability of a sequencing batch reactor (SBR) for treating the liquor (HTCL) derived from hydrothermal carbonization (HTC) of sewage sludge in addition to the influent municipal wastewater. The SBR was fed for 80 days with an increasing mixing ratio HTCL/municipal wastewater. HTCL was used as external carbon source to enhance the denitrification process in the water line of the wastewater treatment plant (WWTP). The feeding of the HTCL caused an overloading in the COD and TKN concentration of the biological treatment equal to, respectively, 25% and 8% (Period II), 50% and 16% (Period III) and 100% and 32% (Period IV). Results revealed that good efficiencies of COD removal were obtained during the entire experimental test, accounting up to 91% in Period IV. Moreover, the removal of TN was improved increasing from 28% in the reference period (Period I), where no HTCL was fed, to 33%, 47% and 64% respectively in Period II, III and IV. Thus, an improvement in the denitrification process was obtained when HTCL was fed to the biological reactor in addition to the influent wastewater. The implementation of the SBR system was supported by nitrate uptake rate (NUR) tests and respirometric assays to evaluate the nitrate removal after the addition of HTCL and the fraction of readily biodegradable COD (RBCOD) and soluble biodegradable COD (sCODbio) on the total COD of the HTCL.

In this work, a modified swirling jet-induced cavitation has been employed for increasing anaerobic digestion efficiency of cattle manure. The hydrodynamic cavitation (HC) treatment improved the organic matter solubilization and the anaerobic biodegradability of cattle manure. The degree of disintegration increased by 5.8, 8.9, and 15.8% after the HC treatment at 6.0, 7.0, and 8.0 bars, respectively. However, the HC treatment at 7.0 bars had better results in terms of methane production. This result may be attributed to the possible formation of toxic and refractory compounds at higher inlet pressures, which could inhibit the methanization process. Further, total Kjeldahl nitrogen content was found to decrease with increasing inlet pressures, as the pH and the turbulent mixing favored the ammonia stripping processes. HC treatment decreased the viscosity of the treated cattle manure, favoring the manure pumping and mixing. Considerations on the energy input due to the HC pre-treatment and the energy output due to the enhanced methane yield have been presented. A positive energy balance can be obtained looking at the improved operational practices in the anaerobic digesters after the implementation of the HC pre-treatment.

A laboratory-scale sequencing batch reactor (SBR) performing partial nitritation – anammox and denitrification was used to treat anaerobic digester effluents. The SBR cycle consisted of a short mixing filling phase followed by oxic and anoxic reaction phases. Working at 25 °C, an ammonium conversion efficiency of 96.5%, a total nitrogen removal efficiency of 88.6%, and an organic carbon removal efficiency of 63.5% were obtained at a nitrogen loading rate of 0.15 kg N m−3 d−1, and a biodegradable organic carbon to nitrogen ratio of 0.37. The potential contribution of each biological process was evaluated by using a stoichiometric model. The nitritation contribution decreased as the temperature decreased, while the contribution from anammox depended on the wastewater type and soluble carbon to nitrogen ratio. Denitrification improved the total nitrogen removal efficiency, and it was influenced by the biodegradable organic carbon to nitrogen ratio. The characteristic patterns of conductivity, oxidation-reduction potential (ORP) and pH in the SBR cycle were well related to biological processes. Conductivity profiles were found to be directly related to the decreasing profiles of ammonium. Positive ORP values at the end of the anoxic phases were detected for total nitrogen removal efficiency of lower than 85%, and the occurrence of bending points on the ORP curves during the anoxic phases was associated with nitrite depletion by the anammox process.

A full-scale anaerobic side-stream reactor (ASSR) for sludge reduction was monitored in terms of sludge production and compared with the previous conventional activated sludge configuration (CAS). A detailed solid mass balance was calculated on the whole full-scale plant to estimate the sludge reduction associated with the ASSR. The activity of the biomass, which undergoes alternation of aerobic and anaerobic conditions, was investigated by the respirometric test. The ASSR promoted a reduction of heterotrophic biomass activity and the substrate consumption rate in the activated sludge implemented with ASSR (AS + ASSR) was 36% smaller than in the CAS period. The solid mass balance indicated a sludge reduction of 28%. During the 270-day operation, the observed sludge yield passed from 0.438 kgTSS/kgCOD in the CAS to 0.315 in the AS + ASSR configuration. The solubilization of chemical oxygen demand (COD), NH4+-N and orthophosphate were verified under anaerobic conditions. The results suggest that the possible mechanisms of sludge reduction were the increase of the system sludge retention time (SRT) by ASSR addition, and the reduction in heterotrophic biomass activity added to the organic compounds' hydrolysis.

Fenton is one of the advanced oxidation processes that can oxide organic compounds efficiently increasing the dewaterability of sludge. This study reports the optimisation of two reagents, Fe

In the last decade, hydrodynamic cavitation (HC) was increasingly used in the field of wastewater treatment. Due to its oxidative capability, HC was applied to treat aqueous effluents polluted by organic, toxic and bio-refractory contaminants, whereas its mechanical and chemical effects have allowed to disintegrate cells of microorganisms in biological applications. Due to their geometries, HC can be detected in some reactors, in which a variation of hydraulic parameters in the fluid such as flow pressure and flow velocity is induced. HC process involves the formation, growth, implosion and subsequent collapse of cavities, occurring in a very short period of time and releasing large magnitudes of power. In this paper, the vast literature on HC is critically reviewed, focusing on the basic principles behind it, in terms of process definition and analysis of governing mechanisms of both HC generation and pollutants degradation. The influence of various parameters on HC effectiveness was assessed, considering fluid properties, construction features of HC devices and technological aspects of processes. The synergetic effect of HC combined with chemicals or other techniques was discussed. An overview of the main devices used for HC generation and different existing methods to evaluate the cavitation effectiveness was provided. Knowledge buildup and optimization for such complex systems from mathematical modeling was highlighted.

Soils contaminated with organic substances is an important issue across Europe: In some areas, these are the main causes of pollution, or the second after contamination from waste disposal. This paper included an experimental application that compared three methods of remediation of contaminated sites, based on electric fields: A single treatment (electroremediation), and two combined treatments, phyto-electrochemical and electrooxidation (a combination of chemical treatment and a DCT&mdash, direct current technology). The contaminated soil was taken from a former industrial area devoted to oil refining, located between two roads: The one national and the other one for industrial use. Nine soil samples were collected at two depths (0.2 and 0.4 m). The initial characterization of the soil showed a density of 1.5 g/cm&sup3, and a moisture of about 20%, regarding grain size, 50% of the soil had particles with a diameter less than 0.08 mm. The electrochemical treatment and electrooxidation had an efficiency of 20% while the two combined methods had efficiencies of 42.5% for electrooxidation (with H2O2) and 20% for phyto-electroremediation (phyto-ER) with poinsettias.

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.

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 t...

Hydrothermal carbonization (HTC) was evaluated as a promising treatment to enhance the biomethane potential during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The OFMSW was carbonized at different conditions and HTC products were tested for biomethane potential into AD. Results proved that the use of HTC liquid and slurry into AD led to an increase in biomethane production up to 37% and 363%, respectively, compared to OFMSW. Methane production increased as the HTC process severity decreased, reaching its maximum at 180 °C, 1 h for both HTC products. Energy assessment demonstrated that the combustion of biogas produced by AD of HTC liquid and slurries covers up to 30% and 104% of the HTC thermal demand, respectively. When the energy from hydrochar and biogas combustion was recovered, the process efficiency reached 60%. Hence, HTC coupled with AD demonstrates to be an efficient way to valorize OFMSW.

In this study, the feasibility of a novel hydrodynamic cavitation (HC) system was evaluated to speed up the biological sludge reduction mechanisms of the anaerobic side-stream reactor (ASSR) process. In the first part of the research, HC was performed on ASSR sludge by using a low pressure swirling jet cavitation system, named Ecowirl – EW 25. The effects of the Ecowirl – EW 25 system, in terms of sludge solubilisation, disintegration degree and microbial activity, were investigated considering two different injection plates, respectively, with two and four injection slots and four different treatment times, from 10 to 80 minutes. The best results were achieved after 80 min of HC treatment, using the plate with two injection slots and with a specific supplied energy (SE) equal to 12670 kJ kg TSS-1. Respirometric tests showed an increase in the readily biodegradable COD through the HC treatment of sludge. Moreover, low endogenous decay rates (bH) were measured on the ASSR sludge for SE lower than 6340 kJ kg TSS-1 revealing that the sludge solubilization was due to a modification in the floc structure rather than a decrease in the biomass viability. In the second part of the research, the solubilized sludge, after HC treatment, was used as carbon substrate for the biological activity of bacteria into the ASSR, such as total phosphate accumulating organisms (TPAOs). Results revealed that the phosphorous releasing and uptake rate, obtained using the HC treated sludge as carbon source, were comparable with those obtained with the addition of a ready biodegradable carbon source such as acetate.

The design of photobioreactors (PBRs) to treat municipal wastewater is in the early stages of development. Kinetics of activated sludge cannot be used for PBRs because biomass differs in composition, growth and decay rates. In this paper, respirometry was extended to a microalgal-bacterial consortium in a long-term PBR treating municipal wastewater. Kinetic and stoichiometric parameters (20 °C) were estimated for endogenous respiration, biodegradable COD oxidation and nitrification. The comprehensive respirometric approach was based on the Oxygen Production Rate (OPR) of photosynthetic microorganisms, and the Oxygen Uptake Rate (OUR) of the overall biomass, including data processing and corrections. The gross OPR (gOPR) was 9.8 ± 0.2 mg O2 g TSS−1 h−1; using microalgae quantified by flow cytometry, the per-cell gOPR was 11 fmol O2 cell−1 h−1. This oxygen was utilized for COD oxidation with rate of 18.0 and 19.3 mg g TSS−1 h−1 under light and dark, respectively. Biomass yield was 0.66 on average, similar to the typical values of activated sludge. The nitrification rate in the dark was 0.92 mg NH4+-N g TSS−1 h−1. The stoichiometric oxygen-over-ammonium coefficient was 4.4 g O2/g N under dark conditions (similar to activated sludge), but lower under light ones (2.8 g O2/g N). The respirometric approach proposed here added experimental kinetic results needed in the PBR design.

Wastewater born microalgal-bacterial consortia in closed photobioreactors (PBRs) have demonstrated high efficiency in pollutant removal, relying only on photosynthetic oxygenation. However, their qualitative and quantitative composition is still poorly understood. This paper describes the extension of flow cytometry in order to analyze a microalgal-bacterial consortium developed in a long-term PBR treating real wastewater. A multi-step procedure was proposed to obtain an accurate flow cytometry (FCM) analysis. Ultrasonication at specific applied energy of 90 kJ L−1 was identified as optimal for sample pre-treatment to recover the maximum number of bacteria and photosynthetic cells while avoiding their disruption. Fluorescence and scattering signals were used to distinguish and quantify microalgae and bacteria. In the tested consortium, bacteria (marked green with SYBR-Green I) were 98% of total cells (on average 1.2E+12 cells/L) while microalgae (having red autofluorescence) accounted for only 2% of total cells (2.8E+10 cells/L). Microalgae were characterized by a biovolume 2 orders of magnitude larger than bacteria, resulting in a photosynthetic biomass quantitatively comparable to bacteria. The proposed FCM approach represents a valuable tool with which to enhance knowledge about the composition and quantification of microorganisms in PBRs, which have not yet been fully understood.

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.

To date, little is known about the start-up of photobioreactors and the progressive development of stable microalgal-bacterial consortia with a view to the full-scale treatment of real wastewater. Two photo-sequencing bioreactors, one inoculated with Chlorella vulgaris (RC) and one with the absence of inoculum (RW), were fed with real municipal wastewater and run in parallel for 101 days. The influence of the inoculation was evaluated in terms of pollutant removal efficiency, excess sludge production, solids settleability and microbial community characteristics. No significant differences were observed in the removal of COD (89 ± 4%; 88 ± 3%) and ammonium (99 ± 1%; 99 ± 1%), mainly associated with bacteria activity. During the first weeks of acclimation, Chlorella vulgaris in RC promoted better P removal and very high variations of DO and pH. Conversely, under steady-state conditions, no significant differences were observed between the performances of RC and RW, showing good settleability and low effluent solids, 7 ± 8 and 13 ± 10 mg TSS/L respectively. Microbiome analysis via 16S rRNA gene sequencing showed that, despite a different evolution, the microbial community was quite similar in both reactors under steady state conditions. Overall, the results suggested that the inoculation of microalgae is not essential to engender a photobioreactor aimed at treating real municipal wastewater.

WAS is a polluting and hazardous waste generated in WWTPs that must be treated to prevent pollution and human health risks. Anaerobic digestion is the most used process for sludge stabilization. However, it must be improved in terms of both speed and extend of degradation. With the purpose of reducing the energy and chemical consumption linked to sludge treatment, in this study, different anaerobic digestion pre-treatments such as low-level mechanical (hydrodynamic cavitation, 2 bar), low-level thermal (50 °C) and low-level alkaline (NaOH, KOH and Ca(OH)2, pH 10) methods, and a combination thereof, were tested as strategies to improve sludge solubilisation. When the pre-treatments were used alone, the alkaline pre-treatment showed the highest sludge solubilisation. Among the alkaline reagents tested, NaOH and KOH led to higher DDPCOD (41.6 and 39.4%), while only 8.4% was achieved by using Ca(OH)2. However, the low-level hydrodynamic cavitation assisted thermo-alkaline pre-treatment was the most efficient in terms of both sludge solubilisation (DDPCOD = 53.0%) and energy efficiency (EE = 64.5 mgΔSCOD kJ−1). The synergetic effects of the combined pre-treatment were also confirmed by the highest release of EPS. Furthermore, cytometric analyses showed that the main mechanism involved in sludge solubilisation for the investigated pre-treatments was flocs disintegration rather than cell lysis.