Sludge Treatment Process Research Articles

Chromium recovery from tannery sludge and its ash, based on hydrometallurgical methods.

The recovery of chromium from tannery sludge and from its respective ash constitutes an alternative process of tannery sludge treatment in order to ensure safe disposal. Chromium recovery was investigated based on simple hydrometallurgical processes, that is, leaching using aqueous solutions of acids. Leaching was applied either directly to air-dried sludge or to its respective ash, which results from thermal treatment of the air-dried sludge under anoxic conditions. The major parameters that influence the effectiveness of the leaching process were investigated to optimize chromium leaching. Specifically, contact time, pH value, temperature, liquid per solid ratio, and leaching agent (H2SO4 or HCl) were tested. Leached chromium, obtained directly from the initial tannery waste after 100 min leaching with H2SO4 at pH 1 and at 60°C, was used for the trivalent chromium precipitation by adding magnesia, calcium hydroxide, and sodium hydroxide as precipitation agents. The results revealed satisfactory leaching of trivalent chromium directly from the air-dried sludge. The chromium content in the solid precipitated using sodium hydroxide was about 59 wt %. In contrast, chromium was difficult to leach from the respective ash.

Effects of stepwise thermal hydrolysis and solid-liquid separation on three different sludge organic matter solubilization and biodegradability

Separate digestion after pretreatment could be a promising process for sludge treatment. In this study, a novel process coupling two-step thermal hydrolysis pretreatment (THP) and separate digestion of liquid and solid fractions was applied on three different sludge to investigate the organic components solubilization and methane production potentials based on mass balance. Results showed that 61.94–69.08% of protein and 84.19–86.75% of polysaccharides were dissolved, while only 35.20–38.55% and 61.61–69.92% were detected in the liquid fraction, respectively. This indicated that not only disintegration and dissolution, but also hydrolysis occurred during THP. Organic matter was mainly dissolved in the first-step THP, and protein and VFAs were the main components. Although separate digestion did not improve the total methane production, the liquid fractions contributed 51.08–73.92% to the sum of liquid and solid fractions. The organic solubilization and biogas production are essentially related to the organic components, instead of the total organic content.

Adsorptive purification of heavy metal contaminated wastewater with sewage sludge derived carbon-supported Mg(II) composite.

A rod-like SDBC-Mg(II) composite was synthesized and optimized in the conditions of 25% Mg(II) loading and 500 °C calcination temperature. As-prepared SDBC-25%Mg(II)-500 adsorbent attained equilibrium in 30 min, with an extraordinary capacity of 2931.76 mg g-1 (Pb(II)) and 861.11 mg g-1 (Cd(II)), revealing a promising adsorbent for the removal of such metals so far. The adsorption kinetics was well described by the pseudo-second-order model while the adsorption isotherm could be fitted by Redlich-Peterson model. Furthermore, SDBC-25%Mg(II)-500 has a high anti-interference and selectivity in the presence of competing ions/other environmental factors and, also effectively eliminates >99% of Pb2+, Cd2+, Ag+ and Cu2+ ions from pond water, lake water and tap water. The adsorption process demonstrated a synergetic adsorption mechanism comprised of ion exchange with Mg(II), coordination with surface and inner carboxylic or carbonyl functional groups and co-precipitations as metal silicates, which is responsible for its superb adsorption performance. Besides, surface carvings of Mg(II) and tunnels on the rods resulting from the sludge carbonization provided a high surface area (91.57 m2 g-1), extra sorption sites and room for easy pollutant diffusion which contributed to surface physical adsorption. Furthermore, this technique demonstrate an alternative pathway that will relieve the burdens of sewage sludge treatment process and turn this solid waste into highly efficient adsorbent for eliminating heavy metal ions from wastewater. This can be considered as a feasible waste resource utilization to meet with the requirement from both ecology and economy for auspicious applications in industries.

Fate of sterols, polycyclic aromatic hydrocarbons, pharmaceuticals, ammonia and solids in single-stage anaerobic and sequential anaerobic/aerobic/anoxic sludge digestion

Emerging contaminants (ECs), such as pharmaceuticals, sterols and polycyclic aromatic hydrocarbons (PAHs) are frequently detected in the environment. ECs are refractory, toxic, tend to bioaccumulate and have a potential to disrupt the endocrine system of living organisms. These compounds are only partially eliminated in wastewater treatment plants (WWTPs). Due to their hydrophobic nature, they tend to accumulate in sludge. However, the fate of the majority of ECs in sludge treatment processes is not fully understood. In this study, the effect of a sequential anaerobic/aerobic/anoxic (AN/AERO/ANOX) digestion and a conventional single-stage AN digestion (as control) was investigated on mixed primary and secondary sludge. Digesters were operated at an overall solid retention time (SRT) of 18 days. The steady-state results have shown that sequential AN/AERO/ANOX digestion configurations improved the removal of three classes of ECs (e.g., sterols, PAHs and pharmaceuticals) by either reducing their accumulation or enhancing their removal. Moreover, sequential AN/AERO/ANOX digestion also achieved 45% less ammonia generation, 20% faster digestate dewaterability and 4% enhanced volatile solids removal compared to single-stage AN digestion.

Catalytic pyrolysis coupling to enhanced dewatering of waste activated sludge using KMnO4[sbnd]Fe(II) conditioning for preparing multi-functional material to treat groundwater containing combined pollutants

Sewage sludge, the major by-product during the primary treatment and subsequent biotreatment of wastewater, is increasingly generated around the world. KMnO4Fe(II) consists both oxidation properties of KMnO4 and flocculation ability by in-situ formed Fe(III) and is widely used in water treatment. In this study, KMnO4Fe(II) was used as chemical conditioners to synchronously improve sludge dewatering performance and catalyze the biomass pyrolysis of waste activated sludge for preparing multi-functional material to remedy arsenic containing groundwater. The results showed that the sludge dewaterability was significantly improved due to the moderate pre-oxidation of extracellular polymeric substances by KMnO4, and then the sludge particles were re-flocculated by Fe(III) generated from KMnO4Fe(II). The conditioned sludge cake was then utilized for preparing sludge-based carbon (Fe-Mn-SBC) which was systematically characterized. The surface area of Fe-Mn-SBC was characteristic of high surface area (100.08 m2/g) which had a great adsorption capacity on arsenic. Besides, Fe-Mn-SBC could effectively oxidize As(III) to As(V), and addition of low dose of H2O2 can further improve total arsenic removal due to catalytic peroxidation of Fe-Mn-SBC. Besides, it was found that the presence of humic acid could inhibit the hydroxy iron formation and compete for the active adsorption sites and then resulted in the decrease in arsenic removal, and the co-existing humic acid could also be removed by adsorption of Fe-Mn-SBC. This work proposed a novel sludge treatment process by combining enhanced sludge dewatering with catalytic pyrolysis for preparing multi-functional materials, and they are promising in treatment of water containing combined pollutants.

Effect of HRT and external resistances on power generation of sidestream microbial fuel cell with CNT-coated SSM anode treating actual fermentation filtrate of municipal sludge

A microbial fuel cell (MFC) with multiwall carbon nanotube (CNT) coated stainless steel mesh (SSM) coated anode (S-MFC) was operated with a filtrate generated by the fermentation of municipal primary sludge. The S-MFC's maximum power density (MPD: 69.8–164.9 W/m3) and energy recovery (ER: 0.15–0.60 kWh/kgCOD) were 7–21 times higher than those (3.8–27.3 W/m3 and 0.01–0.11 kWh/kgCOD) of MFC with a graphite felt as an anode (G-MFC). The microbial communities of S- and G-MFCs varied slightly depending on the electrode material. Chloroflexi (23.5%) was dominant in S-MFC, and Proteobacteria (25.3%) in G-MFC. Fermenting bacteria such as Rhodanobacter lindaniclasticus and Anaerolineaceae bacterium were dominated by continuous non-electrochemically active bacteria invasion because the actual fermentation filtrate was directly utilized as the substrate. Nevertheless, the CNT-coated SSM anode and the fermentation filtrate of primary sludge improved the power generation in MFC, which demonstrates the significant potential of this sidestream process for sludge treatment.

Applications of Advanced Oxidation Technologies for Sludge Treatment

Treatment of sludge is an important issue in water treatment. At present, the traditional sludge treatment process still faces problems such as high sludge production and low solid content, and it is impossible to achieve environmental and economic benefits. Advanced oxidation technology can not only reduce sludge dry base production, but also improve sludge dewatering performance, which has attracted much attention in the field of sludge treatment. On the basis of a brief description of Fenton reagent oxidation, ozone oxidation, wet air oxidation and supercritical water oxidation mechanism, the effects of several advanced oxidation techniques on sludge dry yield and dewatering performance are discussed, and various oxidation methods are introduced. Finally, the advantages and disadvantages of various advanced oxidation technologies are discussed, and the main research directions of advanced sludge oxidation are pointed out.

Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process

Microplastics (MPs) as new pollutants of environmental concern have been widely detected in sewage sludge, and may act as significant vectors for metal pollutants due to their adsorption property. Our findings show that Cd, Pb, and Co, but not Ni, contents in sewage sludge are lower than that of corresponding metal irons adsorbed on sludge-based MPs, indicating that the MPs accumulate such metal pollutants as Cd in the sludge samples. In contrast to virgin MPs, sludge-based MPs are one order of magnitude higher adsorption capacity for Cd, which reaches up to 2.523 mg g−1, implying that there is a considerable enhancement in adsorption potential of the MPs for metals after the wastewater treatment process. SEM analysis shows that sludge-based MPs have rougher and more porous surface than virgin MPs, and FTIR spectra reveal that functional groups such as CO and OH are found on sludge-based MPs. Further, two-dimensional FTIR correlation spectroscopy indicates that CO and NH functional groups play a vital role in the process that sludge-based MPs adsorb Cd, which are not found in virgin MPs. The results imply that increased adsorption potentials of the sludge-based MPs to Cd are attributed to changes in the MP physicochemical properties during wastewater treatment process. In addition, such factors as pH value, and sludge inorganic and organic components also have an effect on the MP adsorption to Cd. Principal component analysis shows that the MPs could be divided into three categories, i.e. polyamide, rubbery MPs (polyethylene and polypropylene) and glassy MPs (polyvinyl chloride and polystyrene). Their adsorption potentials to Cd follow the decreasing order: polyamide > rubbery MPs > glassy MPs. In summary, these findings indicate that MPs may exert an important influence on fate and transport of metal pollutants during sewage sludge treatment process, which deserves to be further concerned.

Effect of sludge char addition on drying rate and decomposition rate of organic waste during bio-drying

To reduce energy consumption in a sludge drying process, sludge treatment process combined with bio-drying and carbonization was newly developed, which reduced the moisture content of the sludge by less than 30%-wet through bio-drying process without adding any auxiliary fuel. In this experiment, bio-drying of dog food, as simulated organic waste sample, in a lab-scale was carried out and effect of sludge char addition on the drying rate and decomposition rate of wet dog food during bio-drying was analyzed. Addition of sludge char to dog food in bio-drying experiment was found to increase the drying rate and to promote decomposition of organic matter. It was also clarified that the drying rate of dog food and decomposition rate of organic matter increased with increasing amount of char addition. Initial amount of filled dog food also influenced drying rate and decomposition rate; the drying rate and decomposition rate increased with increasing dog food amount.

Identification of phosphorus fractions of biofilm sludge and phosphorus release, transformation and modeling in biofilm sludge treatment related to pH

For seeking out potential phosphorus (P) sources, P fractions of biofilm sludge and P release, transformation and modeling in biofilm sludge treatment related to pH were investigated in this study. A laboratory-scale biofilm system was continuously operated to obtain the biofilm sludge. P release batch experiment was carried out by fermentation at different pH. P fraction and transformation were investigated with sequential extraction scheme and P-31 nuclear magnetic resonance spectroscopy. P release performance model was constructed based on extreme gradient boosting (XGBoost) method. Results showed that inorganic Psolid (IPsolid) occupied most in solid phase of raw biofilm sludge (69.21% total Psolid) and the content of releasable and bioavailable P (part of IPsolid and organic Psolid) was 15.56 mg P/g TSS (90.57% of total Psolid), suggesting that biofilm sludge could be a potential P source. The optimum conditions for P release in biofilm sludge treatment process were pH = 5 and pH = 10, respectively, under acidic and alkaline conditions, and the corresponding maximum concentrations of orthophosphate-P were 72.44 mg/L and 76.84 mg/L. Moreover, pH played an important role on P transformation and redistribution in the treatment process. Credible accuracy of P release performance modeling based on XGBoost method was evaluated by root mean square error, mean absolute error and mean relative error, suggesting the feasibility of XGBoost method in modeling P release process, which was beneficial for the application of P release and recovery from biofilm sludge in practical wastewater treatment process.

Critical review of ARGs reduction behavior in various sludge and sewage treatment processes in wastewater treatment plants

It is becoming clear that the wastewater treatment plants (WWTPs) is a key repository for antibiotic resistance genes (ARGs), and WWTPs also represent an important node for limiting ARGs spreading via altering the magnitude and distribution of ARGs in environment. This review provides an overview of the ARGs degradation performance both in sewage sludge and wastewater in WWTPs. The ARGs reduction behaviors during sludge treatment processes including anaerobic digestion (AD), composting, aerobic digestion, bio-drying and air-drying were reviewed, and parameters affecting ARGs reducing efficiency and the probable mechanisms were concluded. In particular, pretreatment approaches such as microwave, thermal hydrolysis and ozone before sludge AD are found to provide the extra benefits for ARGs removal. Additionally, ARGs fates and reduction mechanisms during sewage biological treatments such as anaerobic, aerobic, anaerobic combined with aerobic process and physical-chemical treatment including coagulation, advanced oxidation and disinfection processes were appraised. Furthermore, problems or doubts of previous study are proposed, and some in-depth mechanism researches are anticipated to elucidate the ARGs decay in sewage and sludge treatment process. This can help further enhance the ARGs removal efficiency in WWTPs.

The fate and enhanced removal of polycyclic aromatic hydrocarbons in wastewater and sludge treatment system: A review

As wastewater treatment plant (WWTP) is considered as an important discharge source of polycyclic aromatic hydrocarbons (PAHs) into the environment, many investigations have been carried out to study the behaviors of PAHs in WWTPs. This review focuses on the fate and enhanced removal of PAHs in wastewater and sludge treatment and disposal processes. Firstly, it is found that the occurrence of PAHs in wastewater and sludge depends on the local industrialization and standard. Low-molecular-weight (LMW) PAHs are dominant in wastewater while high-molecular-weight (HMW) ones are dominant in sludge. Then, the fate of PAHs in different treatment processes are discussed in detail. LMW PAHs can be biodegraded by microorganisms while HMW ones are transferred from wastewater to sludge by adsorption. Among sludge treatment techniques, only anaerobic digestion can remove part of PAHs. Compost results in PAHs migratation to other systems, and incineration produces PAHs for incomplete combustion. Also, the enhanced removal strategies of PAHs are reviewed. PAHs removal can be enhanced by increasing their solubility and the activity of microbes, and PAHs generation can be reduced by using Ca-based additives and co-fuel. Finally, the key points for future investigation on PAHs fate and removal in wastewater and sludge treatment are proposed.

Enhancing the digestion of waste activated sludge through nitrite addition: insight on mechanism through profiles of extracellular polymeric substances (EPS) and microbial communities.

Extracellular nitrite has been used to improve the digestion of waste activated sludge (WAS). However, the underlying mechanism remains largely unknown. In this study, WAS was treated with 0.2 gNO2--N/gVSS for 7 days and its performance was compared to that of aerobic and anaerobic treatments. The addition of nitrite had a distinct effect on the reduction of VSS/SS and the accumulation of soluble organics compared to the control reactors. As evident by the variations of extracellular polymeric substances (EPS), nitrite addition had a positive effect on decreasing protein. In particular, the decrease of protein mainly occurred in tightly bound EPS (TB-EPS), which caused sludge disintegration and enhanced sludge reduction. Additionally, the decrease of microbial diversity with nitrite addition was significant compared to the control reactors, accompany with a decrease of live/dead cells ratio and an increase of supernatant DNA concentration. This suggests that nitrite could cause cell death and lysis, resulting in sludge degradation. Thus, nitrite addition enhanced sludge treatment through the combined effect of TB-EPS disintegration and cell lysis. These findings will be useful for the optimization of sludge treatment process based on nitrite addition.

Combination of hydrothermal carbonization and oxy-fuel combustion process for sewage sludge treatment: Combustion characteristics and kinetics analysis

Hydrothermal carbonization (HTC) and oxy-fuel combustion were combined for sewage sludge (SS) disposal for the first time. The combustion characteristics of HTC pretreated SS (hydrochar) under air as well as oxy-fuel combustion atmosphere were investigated by thermal-gravimetric analyzer. On the basis of combustion experiments, the kinetics parameters including energy activation, pre-exponential factor and reaction order were evaluated by Flynn–Wall–Ozawa (FWO) model and Avrami’s theory. The results showed that the hydrochars had higher ignition temperature, higher ignition index and narrower combustion stage than SS, which implied more stable combustion behaviors of the hydrochars than SS. The lower activation energy of the hydrochar obtained from HTC at the temperature of 200 °C demonstrated that the hydrochars were more easily combusted in comparison to SS under identical oxy-fuel conditions. In addition, the ash problems of the slagging and fouling were mitigated by HTC treatment. In oxy-fuel atmosphere, the burnout temperature of the hydrochars was lower than that in air. More importantly, the dewaterability of SS was substantially improved by HTC and more than 30% of drying energy consumption was saved prior to combustion. This study indicated that the combination of HTC treatment and oxy-fuel combustion offered a promising alternative for SS disposal with the benefits of energy consumption and energy recovery.

Importance of sludge conditioning in attenuating antibiotic resistance: Removal of antibiotic resistance genes by bioleaching and chemical conditioning with Fe[III]/CaO

Conditioning can drastically improve the dewaterability of sewage sludge and thus it is widely practiced in most wastewater treatment plants (WWTPs). In WWTPs, various antibiotic resistance genes (ARGs) present in sewage are concentrated in the sewage sludge, but the effect of sludge conditioning on ARGs in sewage sludge remains unclear. Here, we evaluated and compared the effectiveness of four sludge conditioning methods (namely chemical conditioning with polyacrylamide (PAM), chemical conditioning with Fe[III]/CaO, bioleaching conditioning, and chemical acidification conditioning) and an aerobic incubation control in removing 46 target ARGs and intI1 from a municipal sewage sludge. The damage of sludge microbial cells and the change in the sludge bacterial community during the various sludge conditioning treatments were also characterized. The results suggested that the chemical conditioning with PAM and aerobic incubation treatment did not remove ARGs and intI1 from the sewage sludge. The chemical acidification reduced the absolute abundances of most ARGs and intI1, but increased their relative abundances. However, the chemical conditioning with Fe[III]/CaO and bioleaching conditioning reduced both the absolute and relative abundances of most ARGs and removed a majority of extracellular ARGs in the sludge. During sludge conditioning treatments, the sludge microbial cells were severely damaged to decrease the total bacterial biomass in sludge, and accordingly the bacterial hosts carrying ARGs and intI were effectively damaged to reduce the absolute abundances of most ARGs and intI1. In addition, the sludge bacterial community in conditioned sludge determined the relative abundances of residual ARGs. Our findings suggest that sludge conditioning can be an important sludge treatment process in attenuating antibiotic resistance in sewage sludge, and bioleaching and chemical conditioning with Fe[III]/CaO can be employed as effective conditioning ways to reduce ARGs in sewage sludge, potentially limiting their release to the environment.

A Proposal for Recycling the World’s Unused Stockpiles of Treated Wastewater Sludge (Biosolids) in Fired-Clay Bricks

Millions of tonnes of leftover biosolids are increasingly stockpiled every year around the globe. Biosolids are a product of the wastewater sludge treatment process. Stockpiles necessitate the use of large areas of increasingly valuable land. Biosolids have many beneficial uses and are currently utilised in agricultural and land rehabilitation applications. However, it is estimated that 30% of biosolids are unused and stockpiled. A second and seemingly unrelated environmental issue is the massive excavation of virgin soil for brick production. The annual production of 1500 billion bricks globally requires over 3.13 billion cubic metres of clay soil—equivalent to over 1000 soccer fields dug 440 m deep or to a depth greater than three times the height of the Sydney Harbour Bridge. This paper investigates and proposes a practical solution for the utilisation of the world’s excess biosolids in fired–clay bricks. The physical, chemical and mechanical properties of fired–clay bricks incorporating 25%, 20%, 15% and 10% biosolids have been tested. Bricks were produced from three different biosolids samples collected at Melbourne’s Eastern Treatment Plant (ETP 22) and the Western Treatment Plant (WTP 10 & WTP 17–29). Compressive strength testing indicated results ranging between 35.5 MPa and 12.04 MPa for the biosolids-amended bricks. Leachate analysis was conducted on the bricks before and after firing, and the results demonstrate that between 43 and 99% of the heavy metals tested were immobilised inside the fired bricks compared to the heavy metals tested in the raw mixture. All leachate concentrations were found to be insignificant for the biosolids-incorporated bricks tested in this study. Biosolids can have significantly different chemical characteristics depending on the origin of the wastewater and the treatment procedure. Suitable leachate analysis should be undertaken on biosolids and test bricks before large-scale production is approved. Scanning Electron Microscopy (SEM) images illustrate that biosolids-amended bricks have a higher porosity than the control bricks, which corresponds to the lower thermal conductivity values recorded for biosolids-amended bricks. In addition, brick firing energy demands are estimated to decrease by up to 48.6% for bricks incorporating 25% WTP 17–29 biosolids due to the higher organic content of the mixture containing biosolids. The emissions study and comparative Life Cycle Assessment results show that the incorporation of biosolids into bricks is a positive and sustainable alternative approach with respect to all environmental impacts arising from the stockpiling of biosolids and brick manufacturing. Based on the results found in this comprehensive study, this paper proposes the inclusion of a minimum of 15% biosolids content into 15% of brick production in order to completely recycle all the approximately 5 million tonnes of annual leftover biosolids production in Australia, New Zealand, the EU, the USA and Canada. This is a practical and sustainable proposal for recycling all the leftover biosolids worldwide. Utilisation of only 15% of biosolids in brick production would reduce the carbon footprint of brick manufacturing whilst satisfying all the environmental and engineering requirements for bricks.

Operation performance of an A/O process combined sewage sludge treatment and phosphorus recovery using human urine

A novel sewage sludge treatment process is developed in which sludge anaerobically phosphorus (P) released with the temperature control/ultrasonic treatment and recovery with human urine are incorporated to a conventional anaerobic/aerobic (A/O) process. The results showed that temperature affected the anaerobic P release and the maximum orthophosphate (PO4 3-P) release rate was 21.68 mg PO4 3-P/(g MLVSS.h) at 20 °C. The optimal specific energy of ultrasonic treatment was 15,000 kJ/kg TS, at which the solubilization degree of soluble chemical oxygen demand (SCOD) was 37.93%, which verified that the anaerobic sludge flocs were broken and the organic matter was obviously released. Human urine and P-rich sludge stream could be verified as a feasible way of P recovery in the form of struvite. The output of P in the combined A/O treatment process consisted of three pathways (i.e., effluent wastewater, sewage sludge, and P recovery). The influent P could be recovered by 22.84% and about 1.48 g/d potential struvite could be recovered from the anaerobic sludge flow using 0.27 L/d-human urine. The mass balances of COD and nitrogen (N) indicated that the combined A/O process also improved the organic mineralization and the removal of N.

Biocompatibility and biodegradability of polyacrylate/ZnO nanocomposite during the activated sludge treatment process.

Polymer nanocomposites have been widely used in the preparation of coating agents in the leather industry. Considering the complex bio-effect and ecological risk of nanomaterial, research on the biodegradability and biocompatibility of polyacrylate/metal nanocomposites in activated sludge system is of specific significance. We investigated the change of the bacterial community and diversity of activated sludge fed with polyacrylate/ZnO nanocomposites in both low (500 mg COD /L) and high (1000 mg COD/L) doses. COD removal, dehydrogenase activity, and total protein of activated sludge system were monitored in all treatments over 30 days. The results demonstrated that the exposure to both polyacrylate/ ZnO nanocomposite and polyacrylate decreased the dehydrogenase activity at early stage comparing to the control, but had no significant influence on COD removal. Overall, the bacterial communities in activated sludge were resistant to polyacrylate/ZnO nanocomposites, and had higher levels of metabolic activity, protein accumulation and bioavailability when exposed to these chemicals comparing to the control especially at later stages of incubation (15–30 days), which indicated that these polyacrylate/ZnO nanocomposites of certain amount were biocompatible to activated sludge system.

Characterization of fecal sludge as biomass feedstock in the southern Indian state of Tamil Nadu.

Background: Transformative sanitation technologies aim to treat fecal sludge (FS) by thermal processes and recover resources from it. There is a paucity of data describing the relevant properties of FS as viable feedstock for thermal treatment in major geographical target areas, such as India. Methods: This study characterized FS collected from septic tanks in two cities located in the Indian southern state of Tamil Nadu. FS samples were obtained at the point of discharge from trucks in Tiruppur (n=85 samples) and Coimbatore (n=50 samples). Additionally, biosolids obtained from sewage treatment plants (STP) in the cities of Coimbatore and Madurai were characterized. Proximate and ultimate analysis as conducted by the fuel industry was carried out. Results: The average higher heating value (HHV) across all FS samples in Tiruppur (13.4 MJ/kg) was much higher than the value for FS in Coimbatore (5.4 MJ/kg), which was partially attributed to the high ash content of 69% in the latter samples. The HHV in the biosolids samples ranged between 10 and 12.2 MJ/Kg. The average total solids (TS) content for FS was 3.3% and 2.0% for Tiruppur and Coimbatore respectively, while the median TS content for the two cities was 2.3% and 1.2%. The heavy metal content of the ash was found to be below the thresholds for land disposal. Conclusions: This is one of the first studies that has systematically characterized fecal sludge in cities in India and determined its calorific content. We expect these data to serve as input data in the design of thermal processes for fecal sludge treatment.

Effect of Nutrient Removal and Resource Recovery on Life Cycle Cost and Environmental Impacts of a Small Scale Water Resource Recovery Facility.

To limit effluent impacts on eutrophication in receiving waterbodies, a small community water resource recovery facility (WRRF) upgraded their conventional activated sludge treatment process for biological nutrient removal, and considered enhanced primary settling and anaerobic digestion (AD) with co-digestion of high strength organic waste (HSOW). The community initiated the resource recovery hub concept with the intention of converting an energy-consuming wastewater treatment plant into a facility that generates energy and nutrients and reuses water. We applied life cycle assessment and life cycle cost assessment to evaluate the net impact of the potential conversion. The upgraded WRRF reduced eutrophication impacts by 40 percent compared to the legacy system. Other environmental impacts such as global climate change potential (GCCP) and cumulative energy demand (CED) were strongly affected by AD and composting assumptions. The scenario analysis showed that HSOW co-digestion with energy recovery can lead to reductions in GCCP and CED of 7 and 108 percent, respectively, for the upgraded WRRF (high feedstock-base AD performance scenarios) relative to the legacy system. The cost analysis showed that using the full digester capacity and achieving high digester performance can reduce the life cycle cost of WRRF upgrades by 15 percent over a 30-year period.