Waste Activated Sludge Reduction Research Articles

Integrated process of Tetrasphaera-dominated in-situ waste activated sludge fermentation, biological phosphorus removal and endogenous denitrification in single reactor for treatment of wastewater with limited carbon sources

An integrated process of sludge in-situ fermentation, biological phosphorus removal and endogenous denitrification (ISFPR-ED) was developed to treat low ratio of chemical oxygen demand to nitrogen (COD/N) wastewater and waste activated sludge (WAS) in a single reactor. Nutrient removal and WAS reduction were achieved due to Tetrasphaera-dominated sludge fermentation provided organic carbon in extending the anaerobic duration. The WAS reduction efficiency, effluent orthophosphate (PO43−-P) and total inorganic nitrogen reached 28.1 %, less than 0.4 and 7.2 mg/L, respectively. While organic carbon was reduced by 67 %. Tetrasphaera, conventional polyphosphate accumulating organisms (PAOs) stored glycogen, amino acids, and PHA for nutrient removal. Excess energy from fermentation enhanced anaerobic PO43−-P uptake by Tetrasphaera. Tetrasphaera was the dominant PO43−-P removal and fermentation bacteria, working synergistically with conventional PAOs and fermenting microorganisms. This integrated process improves nutrient removal efficiency and reduces operating costs for carbon addition and WAS disposal in wastewater treatment.

Evaluating effects of biochar on anaerobic digestion of dewatered waste activated sludge: Digester performance, microbial co-metabolism and underlying mechanism

Biochar has been proven to be capable of improving the performance of anaerobic digestion (AD). However, the effect of biochar on microbial communities remains ambiguous. In this study, the influence of pH was excluded in a semi-continuous anaerobic digestor for the treatment of dewatered waste activated sludge (WAS) to determine the effect of biochar on microbes. Compared with the control group, the average methane production increased by 24.5% and 23.2% at the organic loading rates (OLRs) of 1.56 and 3.00 gTS/L/d, respectively, in the presence of biochar. This study innovatively found biochar accelerated the enrichment of Methanofastidiosaceae, which competed with Methanobacteriaceae for H2, and its abundance increased from 0.99% at the OLR of 1.56 g TS/L/d to 16.57% and 38.11% at the OLR of 3.00 and 5.60 gTS/L/d, respectively. The efficient metabolic network of f__norank_o__Aminicenantales, syntrophic bacteria, Methanofastidiosaceae and Methanosaetaceae promoted the conversion of WAS to CH4 in the biochar group. In addition, metagenome analysis revealed that biochar optimized the metabolites related to energy conservation and electron transfer, particularly for hydrogenase (frhABG, mbhLHK and hndA-D), confirming that biochar changed the way H2 was involved in methanogenesis. These findings provide novel insights into the direct effect of biochar on microbial evolution and facilitate the reduction of WAS to achieve higher economic benefits in biogas production.

Enhanced hydrolysis/acidogenesis and potential mechanism in thermal-alkali-biofilm synergistic pretreatment of high-solid and low-organic-content sludge

Improving the anaerobic digestion (AD) of high-solid and low-organic-content sludge is imperative for sustainable waste activated sludge (WAS) management. Here, a thermal-alkali-biofilm pretreatment (TAB) was established to treat high-solid and low-organic-content sludge and compared with thermal and thermal-alkali methods. The results showed that TAB drastically improved WAS reduction, hydrolysis/acidogenesis efficiency, and biochemical methane potential. TAB possessed the lowest sludge particle size and the highest surface charge due to the stimulated proteolysis and WAS solubilization, supported by the protease activity test and secondary substrate identification. In addition, the biofilm assistance noticeably accelerated the elimination of autochthonous bacteria in WAS (e.g., Proteobacteria) and facilitated the enrichment of specialized fermentative microorganisms (e.g., Firmicutes) along with relevant functional genes, lying molecular foundation for the enhanced hydrolysis/acidogenesis in TAB. These findings could expand the application of biofilm in the AD of WAS and provide new insight into the pretreatment strategy of high-solid and low-organic-content sludge.

Mechanism insights into enhanced treatment of wasted activated sludge by hydrogen-mediated anaerobic digestion.

In the current study, different forms of added gas including H2, CO2, and mixed gas (VH2:VCO2 = 4:1), as well as different hydrogen partial pressures (0.10, 0.30, and 0.50atm) were investigated for the influence on anaerobic performance in waste activated sludge (WAS) treatment. The mixed gas significantly improved methane production by over 20%, which positively correlated with the hydrogen partial pressure. However, pure H2 (0.5atm) heavily inhibited methane production by 76.5%. Combined with the microbial metabolic activity study, H2 accelerated the hydrolysis process. Afterward, mixing with CO2 accelerated H2 and organic consumption, thus promoting WAS degradation and methane production. Based on the most extra release of organics, the mixed group exerted the superior performance with hydrogen partial pressure at 0.3atm. The microbial community analysis evidenced that mixed gas enriched proteolytic and homoacetogenic bacteria and hybrid-trophic methanogens. By metagenomics study, hydrolysis, acetogenic, and methanogenesis pathways were all enhanced via the exogenous addition of H2 and CO2, sustainably transforming WAS towards CH4. This study discovered the mechanism of the enhanced conversion from WAS to CH4 by exogenous H2 and provided a promising approach for WAS reduction and energy recovery.

A novel partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN) process for real domestic wastewater and waste activated sludge treatment

A novel process was developed for real domestic wastewater and waste activated sludge (WAS) treatment based on partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN). After 246 days of operation, the effluent concentrations of NH4+-N, NO2−-N and NO3−-N were below detection limits (0.1 mg/L), and the effluent concentration of PO43−-P was 0.1 mg/L without the addition of external carbon source in PDA-PFPN system. Moreover, the sludge reduction efficiency reached 48.1% due to fermentation. The nitrite accumulation ratios by ammonia oxidation and nitrate reduction pathway were 60.6% and 87%, respectively. Intracellular metabolites measured by liquid chromatography mass spectrometer (LC-MS/MS) suggested that different intracellular amino acids were stored and consumed at different duration, and intracellular Valine, Glycine and Lysine were not utilized in oxic stage. Results of flow cytometry showed that the proportion of intact cells decreased from 94.7% to 82.9%, and necrotic cells increased from 5.3% to 17.1% with the increase of DNA content in sludge supernatant and cell decay rate, indicating the occurrence of cell death and lysis and leading to WAS reduction. Analysis of transcriptional community composition revealed that partial denitrification bacteria (Thauera), anammox bacteria (Candidatus Brocadia and Candidatus Kuenenia), simultaneous phosphorus removal and fermentation bacteria (Tetrasphaera) and partial nitrification bacteria (Nitrosomonas) coexisted and actually worked in PDA-PFPN system. The novel PDA-PFPN process simultaneously achieved highly efficient nitrogen and phosphorus removal and WAS reduction without the addition of external carbon source, which greatly reduced the operation cost of carbon source dosing and WAS treatment in wastewater treatment.

Key role of soluble microbial products in waste activated sludge reduction by synergetic combination of cocoamidopropyl betaine and alkalinity in the short-time aerobic digestion system

As a widely used ampholytic surfactant, cocoamidopropyl betaine (CAPB) has been improved to enhance waste activated sludge (WAS) reduction in the short-time aerobic digestion (STAD) system, but how system pH value affects the synergetic combined process has not been discussed. This research evaluated how alkalinity affects soluble microbial products (SMP) dynamics and WAS reduction in the synergetic system. After adding CAPB, the biodegradation rate constant of VSS (kVSS), TCOD (kTCOD) and CAPB (kCAPB) were much higher than that of without adding CAPB; pH value at 7.0–8.0 showed the maximum specific oxygen uptake rate (SOUR) of WAS, leading to the highest WAS reduction efficiency. Further study indicated that CAPB can significantly improve the release of extracellular polymeric substances (EPS), leading to the increased SMP concentrations and low molecular weight fractions (MWF) proportions in SMP; more SMP with low MWF fraction led to the increased SOUR, thus further accelerate the WAS reduction; increasing pH could improve the foaminess and solubility of CAPB, thus further improve the organics release and SMP accumulation, which could be quickly removed in the system. This findings lay the foundation of the practical application of the synergetic combination system in WAS reduction.

A novel acetogenic bacteria isolated from waste activated sludge and its potential application for enhancing anaerobic digestion performance

The development of anaerobic digestion (AD) for volatile fatty acids (VFAs) production from waste activated sludge (WAS) is arrested due to low hydrolysis and acidification efficiency. This study proposed to enhance WAS reduction and VFAs accumulation during AD process via bioaugmentation of acetate-producing bacteria. Four acetogens were firstly isolated from a temperature-phased anaerobic digestion (TPAD) system. The acetate production efficiency of different isolates ranged from 15.8 to 73.7 mg acetate/g TOC, in which the bacterial strain NJUST19 was found to be the most effective strain. The results of morphological, biochemical characteristics as well as phylogenetic analysis showed that the isolate NJUST19 was Gram-positive and rod-shaped, catalase-negative, nitrate reduction-positive, methyl red-negative and capable of starch and gelatin hydrolysis, for which the name of Clostridium sp. NJUST19 was proposed. The optimal culture conditions (i.e. initial pH and temperature) were evaluated for their effects on microbe growth of selected NJUST19, and the maximum acetate production was observed at pH 9.0 and temperature of 40 °C. In the case of modified TPAD system inoculated with Clostridium sp. NJUST19, total suspended solids (TSS) removal rate and maximum VFAs accumulation increasing to 35.3% and 4200 mg/L, respectively, which was much higher than that of control (21.9% and 2894 mg/L). These results indicated that Clostridium sp. NJUST 19 is capable of enhancing digestion efficiency with a great benefit for VFAs production, offering potential prospects for bioaugmentation of WAS anaerobic digestion.

The role of a newly isolated strain Corynebacterium pollutisoli SPH6 in waste activated sludge alkaline fermentation.

Alkaline fermentation has been considered as one of the efficient methods for waste activated sludge (WAS) treatment, but usually limited by microbial fermentation activities under extreme pH condition. One newly isolated alkali-tolerant strain Corynebacterium pollutisoli SPH6 was used to assess its potential role and effect on WAS alkaline fermentation process. Results from response surface method showed that the optimal organic nitrogen degradation rate by SPH6 was obtained under temperature of 35 °C, initial pH of 10, shaking speed of 80 rpm, inoculation ratio of 6.5%. Batch-scale experiments demonstrated that, compared with the control group, the inoculation of SPH6 finally achieved higher productions with 13.4% of carbohydrates, 27.1% of protein and 25.4% of total volatile fatty acids (VFAs), and more predominant functional bacteria characterized by high-throughput sequencing, such as genera Acinetobacter in phylum Proteobacteria, Tissierella and Acetoanaerobium in phylum Firmicutes. The strain SPH6 might play a vital role in maintaining and facilitating the growth and diversity of functional bacteria in WAS alkaline fermentation process. It has implied promising practical application of the present strain in enhancing WAS reduction and utilization.

High-efficient nitrogen removal from mature landfill leachate and waste activated sludge (WAS) reduction via partial nitrification and integrated fermentation-denitritation process (PNIFD)

Biological nitrogen removal from mature landfill leachate is ineffective due to the extremely low carbon/nitrogen (C/N) ratio. Moreover, a large amount of waste activated sludge (WAS) is inevitably generated from WWTPs during the municipal sewage treatment process. In this study, an innovative process was developed to enhance nitrogen removal from low C/N (1:1) mature landfill leachate and to reduce the WAS during a 300-day operation. Two sequencing batch reactors (SBRs) were involved in this process. Firstly, the mature landfill leachate was pumped into an aerobic reactor to undergo partial nitrification (PN-SBR). Then, the PN-SBR effluent and WAS were pumped into an anoxic reactor to undergo integrated fermentation and denitritation (IFD-SBR). The pH profile was treated as a real-time parameter to precisely control the duration of the PN and IFD processes. Partial nitrification and integrated fermentation-denitritation (PNIFD) system achieved a total nitrogen removal efficiency of 95.0% and an average nitrogen removal rate (NRR) of 0.63 kg/m3·d during the last operational phase. Due to a variety of refractory contaminants, the effluent COD concentration was 1865.9 mg/L and a 19.7% COD removal efficiency was obtained under an influent concentration of 2324.5 mg/L. Compared with the traditional nitrogen removal process, PNIFD not only decreased requirements for oxygen by 25% and the external organic carbon by 100%, but also achieved simultaneous reduction of external WAS. More than 53.7% of the external sludge was reduced during the IFD-SBR operational cycle, with an average external sludge reduction rate (SRR) of 5.09 kg/m3·d. Fermentation/denitritation related microorganisms, such as Anaerolineaceae, Acidimicrobiaceae and Thauera, accounted for up to 41.5% of the total abundance in the IFD-SBR. Based on the long and stable operation, this study provides a simple and promising approach for synchronous nitrogen removal and WAS reduction.

Promoting waste activated sludge reduction by linear alkylbenzene sulfonates: Surfactant dose control extracellular polymeric substances solubilization and microbial community succession

Short-time aerobic digestion (STAD) was proved to promote the reduction of waste activated sludge (WAS). This study systematically disclosed the influential characteristics and mechanisms of linear alkylbenzene sulfonates (LAS) dosage on the reduction of WAS in STAD system. Flow cytometer (FC) combined with SYTOX Green (SG) dye was used to differentiate extracellular polymeric substances (EPS) release and cell lysis of WAS during STAD process. LAS lower than 0.10 g/g total suspended solids (TSS) brought about EPS solubilization and the decrease of sludge floc size, and the accumulated soluble microbial products (SMP) could be biodegraded by heterotrophs. Moreover, the activity of microorganisms (denoted as specific oxygen uptake rate (SOUR)) and proportion of bacteria functional for LAS and SMP biodegradation dramatically increased, leading to a high LAS biodegradation rate (kLAS) and increased WAS biodegradation rate (kCOD, WAS). Even more LAS (> 0.10 g/g TSS) caused cell lysis, leading to the decreased kTCOD and kLAS, and therefore inhibit the reduction of WAS. High WAS reduction and LAS biodegradation rate were achieved at the LAS dosage of 0.10 g/g TSS in STAD system. This study lays the foundation for improving WAS reduction by optimizing surfactant dose in STAD system.

Achieving energy-efficient nitrogen removal and excess sludge reutilization by partial nitritation and simultaneous anammox denitrification and sludge fermentation process

Energy savings via achieving the reduction of aeration and excess sludge is required to realize energy self-sufficiency in wastewater treatment plants. A novel partial nitritation + simultaneous anammox denitrification and sludge fermentation (PN + SADF) process was operated for nearly two years, during which simultaneous energy-efficient nitrogen removal and waste activated sludge (WAS) reduction was achieved, with a stable nitrogen removal efficiency of 80% and external WAS reduction of 40%–50%. In the PN reactor, presence of ammonia oxidizing bacteria and absence of nitrite oxidizing bacteria ensured the stable nitritation. In the SADF reactor, nitrogen was removed via denitrification and anammox by using nutrients and organics released from WAS solubilization. Comparable performance of the SADF reactor at ambient temperature (12–32 °C) to that at 30 °C indicated a practical application potential for the PN + SADF process. An initial estimation of a full-scale PN + SADF process serving a population of 100000 showed that it could save economy and energy in comparison with conventional nitrification-denitrification process. Despite some challenges in implementation, this paper highlights the potential implication for sustaining mainstream nitritation-anammox towards energy-efficient operation with excess sludge reutilization.

Cocoamidopropyl Betaine Dosage Dependence of Short-Time Aerobic Digestion for Waste-Activated Sludge Reduction

Cocoamidopropyl betaine (CAPB) has newly been found to improve the reduction of waste-activated sludge (WAS) by a short-time aerobic digestion (STAD) process. This work systematically discloses the influences of CAPB dosage on the reduction of WAS by the STAD process. Results showed that CAPB lower than 0.10 g/g of TSS (total suspended solids) mainly increase the organic substances release and low-molecular-weight (MW) fractions proportion via its surfactant action, leading to the increased concentration of soluble biopolymers. The concentration of soluble PO43–-P and NH4+-N increased during the biopolymers release, but gradually decreased in the later stage. Moreover, the specific oxygen uptake rate (SOUR) of digested sludge (denoted as aerobic microorganisms activity) was increased, resulting in the increased biodegradation rate of WAS chemical oxygen demand (kCOD,WAS). A higher amount of CAPB (>0.10 g/g of TSS) led to cell lysis and intracellular polymeric substances (IPS) release, which led to an addi...

Simultaneously enhanced biopolymers production and sludge dewaterability of waste activated sludge by synergetic integration process of short-time aerobic digestion with cocoamidopropyl betaine and calcium oxide

Waste activated sludge (WAS) has seriously threatened the environment safety and the public health due to its rapid growth and complex components. Simultaneously enhanced the biopolymers production and the sludge dewaterability of WAS were investigated by synergetic integration process of the short-time aerobic digestion (STAD) with cocoamidopropyl betaine (CAPB) and calcium oxide (CaO). STAD could improve the biopolymers production by biosynthesis. CAPB could further significantly enhance the biopolymers production and optimized the constituents. CaO (0.1–0.2 g/g TSS) could dramatically enhance the sludge dewaterability by forming a multi-grid skeleton in WAS, while the biopolymers production could almost remain stable. Especially, the synergetic integration process of STAD with 0.1 g CAPB/g TSS for 8 h and 0.1 g CaO/g TSS could cost-effectively enhance both the biopolymers production and the sludge dewaterability. The produced biopolymers showed strong adsorbability for heavy metals (eg, 375 mg Cu2+/g biopolymers). Accordingly, the developed novel process is of big significance for resource utilization and volume reduction of WAS.

PH dependent of the waste activated sludge reduction by short-time aerobic digestion (STAD) process

The short-time aerobic digestion (STAD) process has been found to be a unique and significant technique for the stabilization of waste activated sludge (WAS), but the influences of the system pH on the STAD process was unclear. This study systematically disclosed the influences of the system pH on the STAD process of WAS. Under neutral or weak alkaline conditions, although the biodegradation rates of VSS (~0.0085 h−1) were low, high biodegradation rates of TCOD (kTCOD) (~0.0096 h−1) were achieved. Less releases of the biopolymers from the WAS led to low concentrations of STOC, UV254, the low MW organic matters, NH4+ ‐ N and PO43− ‐ P in the supernatant. However, the appropriate pH for the microorganisms improved SOUR, indicating that the released substances were further reused or biodegraded by the microorganisms. Under acidic or alkaline conditions, the biodegradation rates of VSS (0.009–0.019 h−1) and TCOD (kTCOD) (0.005–0.009 h−1) were opposite with those under neutral or weak alkaline conditions. The releases of the biopolymers were increased, leading to high concentrations of STOC, UV254, the low MW organic matters, PO43− ‐ P and NH4+ ‐ N in the supernatant. However, the extreme pH inhibited the microbial activity. The SOURs were only 0.0097 h−1 and 0.0053 h−1 for system pH of 8.0 and 4.0, respectively. Accordingly, neutral and weak alkaline conditions should be more suitable for the STAD process of WAS. This work lays the foundation for optimizing system pH for the reduction of WAS in STAD system.

Enhancing phosphorus release from waste activated sludge by combining high-voltage pulsed discharge pretreatment with anaerobic fermentation

Abstract The effect of high-voltage pulsed discharge (HVPD) pretreatment on waste activated sludge (WAS) for phosphorus (P) release enhancement via anaerobic fermentation (AF) was studied. Batch tests were performed to investigate the P release via HVPD pretreatment and AF. The P release could be enhanced by a 26.7% soluble ortho-P [SOP(L)] concentration increase via HVPD + AF compared with the control sample (AF of WAS without pretreatment). The HVPD and AF contributed 42.2% and 57.8% to the total SOP(L) increase, respectively. The P speciation analyzed using the Standards, Measurements, and Testing extraction protocol indicates that the decrease of non-apatite inorganic P (NAIP) in the solid phase is consistent with the increase of SOP(L) in the liquid phase and the release of poly-P from WAS could be enhanced due to the destruction of sludge flocs by HVPD. In addition, removal rates of 23.8% of total suspended solids (TSS) and 34.3% of volatile suspended solids (VSS) were calculated for the HVPD-pretreated solid phase, which suggests that the soluble organics production and WAS reduction were also enhanced via HVPD + AF. The results reveal that HVPD pretreatment is a promising method for the recovery of P from WAS and WAS reduction.

Pre-recovery of fatty acid methyl ester (FAME) and anaerobic digestion as a biorefinery route to valorizing waste activated sludge

This study presented the effects of lipids extraction from waste activated sludge (WAS) via in-situ transesterification on anaerobic digestion performance. The nonpolar transesterified product (TP) yield through the extraction was 9.68% of the dried mass of WAS and its fatty acid methyl esters (FAMEs) content was 78.45%. Pre-extraction of lipids lead to the solubilization of the sludge. The biochemical methane potential (BMP) test exhibited that both the extent and rate of methane production increased by 3.65 times after the pre-extraction of lipids. Overall solid reduction of WAS through the series of lipid extraction and anaerobic fermentation was enhanced by more than 5 times compared to that of control. Based on energy balance, the strategy proposed in this study could be an alternative biorefinery route to valorizing WAS with a simultaneous production of FAMEs as a biodiesel feedstock and biogas.

Achieving simultaneous nitrogen removal of low C/N wastewater and external sludge reutilization in a sequencing batch reactor

An integrated partial nitrification, sludge fermentation and denitrification process in a sequencing batch reactor (PNSFD-SBR), was developed to enhance nitrogen removal from domestic wastewater with low C/N (i.e. SCOD/TN) between 2 to 3 and to reutilize/reduce external waste activated sludge (WAS). Average ammonium removal efficiency of 95.9%, total nitrogen removal efficiency of 93.5%, and external WAS reduction rate of 21.6% was achieved during long-term experiment at 30±1°C. Real-time pH-DO (dissolved oxygen) monitor and control played an important role in the PNSFD achievement. A batch test indicated that micro-aeration (less than 1mg/L) sustained partial nitrification, which further facilitated subsequent sludge fermentation and denitrification processes. Moreover, Illumina MiSeq analysis demonstrated the predominant bacteria were Rhodocyclaceae, Anaerolineaceae and Saprospiraceae on family level and they were key to partial nitrification, denitrification and sludge fermentation, by which the feasibility of PNSFD process to achieve simultaneous nitrogen removal and external WAS reutilization/reduction was verified.

Short-cut waste activated sludge fermentation and application of fermentation liquid to improve heterotrophic aerobic nitrogen removal by Agrobacterium sp. LAD9

Abstract Conventional anaerobic waste activated sludge (WAS) fermentation has been proved efficient in WAS reduction and internal carbon sources (e.g. volatile fatty acids) production for heterotrophic aerobic nitrogen removal, but to be time-consuming (within weeks). This study revealed similar efficiency for nitrogen removal enhanced by Agrobacterium sp. LAD9 capable of heterotrophic aerobic nitrogen removal using products from short-cut WAS fermentation process improved by thermal-alkaline pretreatment within only 14 h. Bench-scale experiments demonstrated that about 30% organics could be extracted for carbon sources recovering and sludge reduction during short-cut WAS fermentation, and addition of CaO, MgCl2·6H2O and polyacrylamide sequentially into fermented WAS exhibited better sludge dewaterability and higher carbon recovery efficiency. With the similar initial biomass concentration, the activated-sludge system with addition of LAD9 and short-cut fermentation products (chemical oxygen demand to nitrogen (COD/N) = 9) excellently performed with nitrogen removal efficiency of 86.4% within 6 h, much higher than those of 74.2% with addition of LAD9 only (COD/N = 6) and 52.5% with neither LAD9 nor short-cut fermentation products (COD/N = 6). The proposed system modified with LAD9 is of great potential for on-site reduction, reuse and recycling of WAS, and more efficient than conventional nitrogen removal systems by using short-cut WAS fermentation liquid.

Effects of various pretreatments on biological sulfate reduction with waste activated sludge as electron donor and waste activated sludge diminution under biosulfidogenic condition

The current study focused on the influences of various pretreatments, including alkaline, ultrasonic and thermal pretreatments on biological sulfate reduction with waste activated sludge (WAS) as sole electron donor. Our results showed that thermal and ultrasonic pretreatments increased the sulfate reduction percentage by 14.8% and 7.1%, respectively, compared with experiment with raw WAS, while alkaline pretreatment decreased the sulfate reduction percentage by 46%. By analyzing the WAS structure, particle size distribution, organic component, and enzyme activity after different pretreatments, we studied the effects of these pretreatments on WAS as well as on the mechanisms of how biological sulfate reduction was affected. The reduction of WAS and variation of WAS structure in the process of sulfate reduction were investigated. Our results showed that biosulfidogenesis was an efficient method of diminishing WAS, and various pretreatments could enhance the reduction efficiency of volatile solid in the WAS.

Underlying Mechanistic Principles, Performance Evaluation and Proposed Modeling Approach for Selected Waste Activated Sludge Reduction Technologies

Underlying Mechanistic Principles, Performance Evaluation and Proposed Modeling Approach for Selected Waste Activated Sludge Reduction Technologies