Sludge Batch Research Articles

Use of polysorbate 20 and sodium thiosulfate to enhance sewage sludge dewaterability by bioleaching

Dewatering of sludge is a key problem that must be solved in the sewage sludge disposal industry. In this study, a series of process optimization tests were conducted to learn how to improve sludge treatment. The optimum process of sludge leaching treatment was studied in a specially designed 100-L reactor system. Four factors were investigated and nine batches of bioleaching tests were run at three levels of these factors. Orthogonal experiments showed that the effect of sludge return ratio and aeration rate on the sludge moisture content was significant and hydraulic retention time (HRT) had a clear effect, but nutrient types had a reduced effect on the moisture content of sludge. The primary and secondary order of each factor is reflux ratio > aeration rate > HRT > nutrient type. Under the optimal process, three batches of sludge were processed and the moisture content of the filter press cake was reduced to less than 60%, the organic matter content reduced to below 5%, and the concentration of heavy metals (Cu, Zn, Pb, and Cr) was much lower than the agricultural standard limit, which is suitable for landscaping, composting, and incineration power generation and other resource applications.

Increasing plant phosphorus availability in thermally treated sewage sludge by post-process oxidation and particle size management

Thermal conversion of phosphorus (P)-rich waste materials such as sewage sludge offers several advantages: generation of bioenergy, concentration of plant nutrients and the destruction of organic pollutants. Different thermal processes modify the feedstock’s chemical and physical structure in differing ways, which also affects P speciation and plant availability in the residual ashes or carbonization products. This study assessed to which extent the P plant availability of ashes and chars produced from one batch of sewage sludge by incineration, pyrolysis or gasification was affected by particle size management and post-process oxidation. Overall, a smaller particle size of the materials as well as post-process oxidation of non-oxidized materials increased the amount of plant-available P in the soil. In a pot experiment, all the materials increased plant biomass compared with the untreated control, but the pyrolysis chars had a substantially greater fertiliser value than the gasification ashes, while the two tested incineration ashes differed in their P fertilizing effect. P availability in non-oxidized materials was partly related to lower process temperatures and lower levels of crystallinity. However, downstream oxidation simultaneously increased crystallinity and P availability in a pyrolysis char and gasification ashes, resulting in an increase in plant P uptake of up to 60%. Results indicate that the oxidation of poorly soluble Fe-phosphates may contribute to the positive effect on P availability. The results suggest that changes to the design and settings of the thermal conversion processes of sewage sludge offer considerable potential for improving P availability in the residual material.

Comparison between the performance of activated sludge and sequence batch reactor systems for dairy wastewater treatment under different operating conditions

The main purpose of this study was to investigate the effect of operating conditions on the performance of two methods used for dairy wastewater treatment. First, conventional activated sludge (AS). Second, conventional sequencing batch reactor (SBR). On one side, the study included the comparison between the two basic systems. On the other side, it studied the influence of adding plastic media on both systems. The modified systems are known as biofilm conventional activated sludge (BAS) and biofilm sequencing batch reactor (BSBR). Four pilot-scale bioreactors, were operated in parallel under different conditions of temperature; 20, 35 and 45 °C. Synthetic dairy wastewater was used with characterizations of COD; 5000 mg/l, NH3-N; 250 mg/l and TP; 50 mg/l. The results recorded that the optimum temperature was 35 °C where removal efficiencies for COD were (93.52%, 96.63%, 94.74% and 97.79%), (89.01%, 91.14%, 90.45% and 93.22%) for NH3-N, and the concentration of NO3-N in effluents was (7.56 mg/l, 10.58 mg/l, 8.72 mg/l and 14.12 mg/l) for AS, BAS, SBR and BSBR respectively. At temperature equals to 45 °C; the oxygen consumption recorded the highest level of consumption, it was (1.07 mg/l, 1.64 mg/l, 0.98 mg/l and 1.23 mg/l) for AS, BAS, SBR and BSBR respectively. The results indicated that the sludge settleability was enhanced with the decrease of temperature. Furthermore GPS-X simulator was employed to predicting the performances of the biological systems under high COD concentrating reaching up to 17500 mg/l. GPS-X results indicated that SBR effluent could comply with Egyptian standard NO 2000. An overview, comparing with various treatment systems, it can be concluded that the SBR was the optimum treatment method for dairy wastewater based on the investigated conditions.

Wastewater Treatment Processing of Silver Nanoparticles Strongly Influences Their Effects on Soil Microbial Diversity.

Silver nanoparticles (NPs) are entering soils with biosolids via wastewater treatment, and on-route, undergo changes (e.g., sulfidation) that alter silver bioavailability and toxicity. While additions of fresh Ag-NPs to soil have been show to influence bacterial diversity, it is unclear whether these effects are representative of realistic exposure pathways. To investigate the effects of wastewater treatment processing on the ecotoxicology of Ag-NPs, we ran sequencing batch reactors for 28 d to produce three batches of sludge: (1) a control, (2) Ag-NP sludge, and (3) AgNO3 sludge. The effects of processed silver on the diversity and composition of soil bacterial and fungal communities were compared to those of fresh Ag-NPs, Ag2S-NPs, and AgNO3, which were added with the control sludge, at two concentrations (1 and 10 mg Ag kg-1 dry soil) over time (3, 7, 30, and 90 d). The effects of processed Ag-NPs on the composition of soil bacterial communities were larger and more persistent than those of fresh Ag-NPs, Ag2S-NPs, and AgNO3. Treatment effects on fungi were relatively minor. These findings suggest that the potential ecological impacts of Ag-NPs entering soils via more realistic exposure pathways (e.g., sludge) are underestimated when extrapolated from studies that focus on applications of fresh Ag-NPs.

Comparative evaluation of the biochemical methane potential of waste activated sludge acetic acid and cellulose substrates under mesophilic and thermophilic anaerobic digestion

Knowing the biochemical methane potential of a substrate to biogas production is a preliminary to possible selection of the pre-anaerobic digestion technology and identifying the optimum reaction time. Following standard method to reactor assembly, feed preparation and monitoring of the specific methane yield, the two temperature systems are compared among substrates. As a result, the rate of biochemical methane yield from the waste activated sludge anaerobic digestion in the thermophilic case is much faster than the mesophilic. The specific methane yield and volatile solid removal of the waste activated sludge batch anaerobic digestion is 74% of the theoretical and 81% for the thermophilic while it is 57% theoretical and 76% for the mesophilic, respectively. However, the best methane yield is recorded for the acetic acid followed by the cellulose and sludge substrates, signifying the importance of sludge pretreatment to enhance degradability in anaerobic digestion. Also, the optimum reaction time for thermophilic and mesophilic systems is different.

Agricultural use and pH correction of anaerobic sewage sludge with acid pH

Agricultural use is the main way of recycling sewage sludge. Besides providing nutrients and organic matter to crops and soils, it is an important alternative for recycling this residue. However, problems during the sewage treatment process may generate sludge batches with an acidic pH. Thus, it is essential to understand the consequences of using such sludge on soils and plants, and to explore ways to overcome this limitation. The objective of this study was to evaluate addition rates of anaerobic sewage sludge (ASS) with acidic compositions on the soil fertility and performance of lettuce plants. Additionally, a methodology for pH correction of ASS with acidic pH is proposed. An agronomic experiment was conducted in a greenhouse using seven addition rates of ASS (0.0, 0.25, 0.5, 1, 2, 4 and 8 g kg−1 in dry basis), treated with an additional step of disinfection (solarization), and applied in an Albaqualf soil cultivated with lettuce (Lactuca sativa). Soil and leaf chemical composition, as well as chlorophyll index and the dry matter of lettuce leaves were evaluated. Failures during the acidogenesis phase of the anaerobic digestion process were probably the cause of ASS acidification. Although this ASS increased soil fertility indicators and plant dry matter, it significantly reduced soil pH, thereby requiring a complementary assay to correct its pH up to 6.0, which was achieved through liming. Anaerobic sewage sludges with an acidic pH can be effectively used in agriculture after being dried and disinfected through solarization, followed by pH correction, avoiding negative impacts on soil chemical attributes and plant response.

Waste-organics supported treatment of nitrogen-rich digester supernatant

The goal of the study was to treat nitrogen-rich digester supernatant for water reuse in a three-stage system with an aerobic granular sludge batch reactor (GSBR), a post-denitrification (P-D) reactor and a membrane module. In the study, the effects on treatment efficiency of organic loading and aeration mode in the GSBR, the type of waste organics in P-D and the parameters of filtration were investigated. Denitrification efficiency was highest in the GSBR operated with 2 anoxic phases in the cycle and at 1.8 g COD/(L·d), but in this reactor, the N-NO2−/N-NO3− ratio was the highest (2.43). Shortening the anoxic period in the cycle and increasing organic loading to 2.1 g COD/(L·d) decreased nitrite accumulation in the effluent (the N-NO2−/N-NO3− ratio of 0.23). The effluents with different N-NO2−/N-NO3− ratios were subjected to P-D with glycerin fraction (GL), distillery residue (DR) and volatile fatty acids (VFAs) as waste organic sources. P-D of nitrate-rich GSBR effluent with VFA resulted in denitrification efficiency up to 97.9 %, and followed by microfiltration produced a final stream that could be directly discharged to the environment or used for irrigation. The use of P-D with GL and DR was most efficient for the treatment of GSBR effluent in which nitrite predominated. Denitrification efficiencies reached 26.7 % with GL and 22.0 % with DR. After polishing by ultrafiltration, the final stream had low COD and color, no turbidity, high concentrations of NOx, and could be used for algae growth for bioproduct recovery.

Examining the behavior of crop-derived antibiotic resistance genes in anaerobic sludge batch reactors under thermophilic conditions.

The consumption of transgenic crops and their by-products has become increasingly common in the United States. Yet, uncertainty remains regarding the fate and behavior of DNA within food matrices once it exits the digestive track and enters into wastewater treatment plants (WWTPs). Because many transgenic crops have historically contained antibiotic resistance genes as selection markers, understanding the behavior and uptake of these transgenes by environmental microbes is of critical importance. To investigate the behavior of free transgenic crop DNA, thermophilic anaerobic batch reactors were amended with varying concentrations of transgenic crop genes (i.e., LUG, nptII, and bla) and the persistence of those genes was monitored over 60 days using quantitative PCR. Significant levels of nptII and bla were detected in extracellular DNA (eDNA). Furthermore, LUG maize marker genes were also detected in the control reactors, suggesting that other crop-derived transgenes contained within digested transgenic foods may also enter WWTPs. Possible bacterial transformation events were detected within the highest dose treatments at Days 30 and 60 of incubation. These findings suggest that within the average conventional digester residence times in the United States (30 days), there is a potential for bacterial transformation events to occur with crop-derived transgenes found in eDNA.

Analysis of Solid residue and Flue Gas from Thermal Plasma Treatment of Petroleum Sludge

The traditional methods of disposing of petroleum sludge are short of providing the much-needed benign treatment. A more robust treatment technique is desirable. In this investigation, a laboratory-scale thermal plasma reactor was developed and was used to treat 20 g per batch of petroleum oily sludge. The output current and the plasma temperature measured using an infrared thermometer range were 5 – 200 A and 356 – 1694 °C respectively. After the plasma treatment, the morphology of the sludge transformed from jelly-like to crystalline solid structure. A mass and volume reductions of 36.87 – 91.40% and 59.59 – 94.52%, respectively, were achieved in a treatment period of 2 – 5 min. A Total Organic Compound (TOC) reduction of 21.47 – 93.76% were equally achieved in same treatment period. Heavy metals concentration in the sludge were increased after the plasma treatment, whereas, Ni and Pb manifested only in the solid residue. The result of the leaching test of heavy metals from the solid residue is within the US EPA recommended level for secure landfill. The major components of the flue gas were H2, CO, CO2 and H2O with small quantities of CH4, C2H2 and C2H4. The flue gas has an LHV range of 7.40 – 7.86 MJ/Nm3 with a corresponding cold gas efficiency of 25.22 – 51.90%. Based on the operating cost estimation, a profit margin of $ 0.76 /kg of sludge was established. The thermal plasma technique is, therefore, an alternative treatment method for treating petroleum sludge.

Treatment of Liquid Phase of Digestate from Agricultural Biogas Plant in a System with Aerobic Granules and Ultrafiltration

Management of digestate from manure co-digestion with a very high chemical oxygen demand (COD) to nitrogen ratio and high nitrogen loads are a major bottleneck in the development of agricultural biogas plants. The liquid phase of digestate mixed with municipal wastewater was treated in aerobic granular sludge batch reactors at cycle lengths (t) of 6 h (GSBR6h), 8 h (GSBR8h), and 12 h (GSBR12h), corresponding to nitrogen loads of 1.6, 1.2, and 0.8 g/(L·d). Thauera sp., Lacibacter sp., Thermanaerothrix sp., and Planctomyces sp. predominated in granules favoring effective granule formation and nitrogen removal. Increasing cycle lengths (t) significantly decreased proteins in soluble fraction of extracellular polymeric substances (EPS) in granules and increased polysaccharides in tightly bound EPS that resulted in higher granule diameters and higher COD removal. In GSBR6h, heterotrophic nitrification/denitrification was very efficient, but ammonium was fully oxidized in the last hour of the cycle. So in further studies, the effluent from GSBR8h was subjected to ultrafiltration (UF) at transmembrane pressures (TMPs) of 0.3, 0.4, and 0.5 MPa. A GSBR8h-UF system (TMP of 0.4 MPa) ensured full removal of total Kjeldahl nitrogen (TKN), suspended solids, and substantial reduction of COD and color with good permeate flux. The NOx-rich (about 250 mg/L), clear permeate can be reused in line with assumptions of modern circular economy.

Assessment of Cadmium and Lead in Dried Sewage Sludge from Lubigi Feacal Sludge and Wastewater Treatment Plant in Uganda

Sludge contains organic and inorganic compounds including traces of heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), nickel (Ni), chromium (Cr) and others. These metals restrict the use of sludge in agriculture because their accumulation is harmful to the environment and particularly the food chain. Cadmium and lead are among the most common heavy metals found in municipal wastewater treatment plant sludge. They are capable of bioaccumulation in plant tissues like roots and leaves and are non-biodegradable and therefore they remain in the sludge which is disposed on land or used as fertilizers on farms. The presence of heavy metal pollutants serves as a great threat to soils and also makes plants grown on such soils unfit for animal and human consumption as they may have detrimental effects to animal and human life. For instance, Pb and Cd are known to be human carcinogens. This study therefore aimed to investigate the levels of Cd and Pb in the treated dry sludge from Lubigi Feacal Sludge and Wastewater treatment plant located in Kawempe division, Kampala city, Uganda so as to ascertain its safety for use on agricultural lands. Two batches of samples were collected and analyzed at Government Analytical laboratory in Wandegeya, Uganda. The acid digested sludge samples were analyzed using Atomic Absorption Spectroscopy (AAS) method. The average concentrations of Pb found in collected sludge samples, batch 1 (11.912 mg/kg dm) and batch 2 (5.304 mg/kg dm) were far below the Environment Protection Agency (EPA) maximum permissible concentration (840 mg/kg) for any land application. Cadmium was not detected in all the sludge samples collected; there is an implication that it is either completely absent in the sludge generated by the plant or present but far below detectable levels. The sludge generated from Lubigi fecal sludge and wastewater treatment plant is therefore safe for application on agricultural lands as far as Pb and Cd concentrations are concerned.

Treatment of the liquid phase of digestate from a biogas plant for water reuse

Biogas plants struggle with managing nitrogen-rich digestate from manure co-digestion. In this study, the biologically treated liquid phase of digestate from an aerobic granular sludge batch reactor (GSBR) containing oxidized nitrogen forms (NOx), phosphorus, COD and total suspended solids was post-denitrified (P-D), and then ultrafiltered. In P-D, various hydraulic retention times (from 10 to 60 h) and biomass concentrations (from 6 to 14 g MLSS/L) were tested. Then, waste glycerin (GL) was added to the P-D reactor at a CODGL/NOx ratio of 1.1, causing a large number of phosphate-accumulating and denitrifying Janibacter sp., and PHB-accumulating and denitrifying Paracoccus sp. and Thauera sp. to be present in granules, which improved nutrient removal. The effluent was ultrafiltered at 0.3 and 0.5 MPa. After biological treatment supported with GL and followed by ultrafiltration, the purified liquid phase of the digestate met FAO standards for water reuse for irrigation.

Biodegradation and Metabolism of Tetrabromobisphenol A (TBBPA) in the Bioaugmented Activated Sludge Batch Bioreactor System by Heterotrophic and Nitrifying Bacteria.

Tetrabromobisphenol A [2,4'-isopropylidenebis(2,6-dibromophenol)] has been identified in wastewater samples collected from the Guelph municipal wastewater treatment plant (GWWTP). In order to assess the kinetics and metabolic mechanisms of the dissolved TBBPA, bench scale experiments were completed with batch bioreactors. The biodegradation test was conducted by taking aerobic sludge from the conventional activated sludge reactor (CAS) and membrane bioreactor (MBR), and bioaugmenting both reactors with soil based strains of Bacillus brevis and Bacillus pumilus. This novel biodegradation process showed that the CAS bioreactor had a biodegradation rate of 0.127 d-1, while the sludge from the MBR had a biodegradation rate of 0.171 d-1. This is the first reported aerobic biodegradation of TBBPA by heterotrophic and nitrifying bacteria in an activated sludge bioreactor system. A tentative biotransformation metabolic scheme for TBBPA biodegradation and metabolite formation has been proposed as well.

Performance Evaluation of Sequencing Batch Reactor and Conventional Wastewater Treatment Plant based on Reliability assessment

Baghdad city has been faced numerous issues related to freshwater environment deteriorations due to many reasons, mainly was the discharge of wastewater without adequate treatment. Al-Rustamiya Wastewater Treatment Plant (WWTP) have been constructed among many plants in Baghdad city to reduce the amount of wastewater discharged into natural environment and its subsequent adverse effects. This study was conducted to evaluate the performance of the plant which consist of a conventional activated sludge (CAS) and sequencing batch reactors (SBR) systems as secondary treatment units and its ability to meet Iraqi specifications. A reliability level determination and analysis also were conducted to find the plant's stability and its capability to produce effluents that met the local standards. Coefficient of Reliability (COR) determination was done for effluent's concentrations of BOD5, COD, and TSS obtained from Al-Rustamiya WWTP for two years' data operation (2015-2016), using Iraqi standards concentrations. Generally, the results showed the effectiveness of Al-Rustamiya WWTP-(CAS and SBR system) was a major concern due to inadequate sewage treatment and that the plant effluents of both systems selected parameters BOD5, COD and TSS are not meeting the Iraqi standards due to many problems mainly were operational problems result in overall poor performance.
 

Impact of High-Nitrogen Leachate on Microfauna of Aerobic Granular Sludge.

The microfauna communities present in aerobic granular sludge reactors (e.g., granule sludge batch reactor or GSBR) that are used to treat landfill leachate were studied to determine which taxons are useful as process performance indicators. Communities were analyzed during four periods: a stable reactor operation period at a temperature of 29 °C, a transitional period of biomass adaptation at a temperature of 25 °C, an additional period of stable reactor operation at 25 °C, and at 25 °C after a period of lowered dissolved oxygen concentration. The results indicate that Vorticella infusionum and telotrochs were the taxons most sensitive to environmental changes in the GSBR, showing potential as biological indicators of ammonium overload and process destabilisation. Other taxons had similar abundance, despite changing environmental conditions in the bioreactor.

Degradation of Cocaine and Benzoylecgonine in Sewage Sludge Batch Tests

The degradation studies of cocaine and its principal metabolites, benzoylecgonine, as emerging pollutants were carried out using various sludge types collected from the RAF Molesworth Sewage Treatment Work (STW) to determine their distribution and persistence in aquatic environment. The methodology, initially characterized the various sludge types before the laboratory batch tests were carried out at different temperatures and times. The results, after 3 hours equilibration of batch samples, showed the removal rates for cocaine and benzoylecgonine to be 91.0% and 90.6%, respectively. The partition coefficients (Kd) for the two substances ranged from 2.7 – 31.9 Kg L-1. Degradation of compounds was found to be both biotic and abiotic and the two processes produced many short chain compounds and several metabolites that include cocaethylene and ecgonine methylester. Also at 4 ± 0.5o C, the degradation of substances occurred slowly, at 5 and 10% but was relatively greater at 19 ± 0.5o C. Compounds degradation was also influenced by both extracellular and intracellular enzyme activities. The batch study is an innovative method in calculating degradation rates of compounds from sewage treatment works. The capabilities of generating removal rates of drugs have also been clearly demonstrated in this work and can be applied to any organic compounds in real life (STWs) situations

Biogas production from anaerobic co-digestion of cow manure with kitchen waste and Water Hyacinth

The prime objective of this paper was to analyze and compare biogas production from various sources of waste material. The Renewable Energy Policy envisions that 5% of total energy production needs to be achieved by 2015 and 10% by 2020. This work focuses on the comparative study of the production of biogas through anaerobic co-digestion utilizing abandoned resources of biomass. Materials under study were Cow manure, Sewage Sludge, Kitchen Waste & Water Hyacinth. Experiments were conducted under mesophilic condition (37 °C) with 1.5 wt%NaOH to obtain the desirable pH. The loading ratio of each batch was maintained as 1:1 on both experiments. Kitchen Waste and Cow Manure showed promising results till about the 120th hour following plummeting production of biogas. Total production for 1 L batch of Water Hyacinth, Cow Manure & Sewage Sludge was 812 ml with 65%Methane, 14%CO and 21%other gases obtained after 800 h, while Kitchen Waste & Cow Manure provided 335 ml consisting of 60%Methane, 18%CO & 22%other gases within the same time frame. Results indicated that addition of Sewage Sludge with the widely used Cow Manure can lead to accelerated reaction, increased production and an improved methane content.

Sludge from paper mill effluent treatment as raw material to produce carbon adsorbents: An alternative waste management strategy

Pulp and paper industry produces massive amounts of sludge from wastewater treatment, which constitute an enormous environmental challenge. A possible management option is the conversion of sludge into carbon-based adsorbents to be applied in water remediation. For such utilization it is important to investigate if sludge is a consistent raw material originating reproducible final materials (either over time or from different manufacturing processes), which is the main goal of this work. For that purpose, different primary (PS) and biological sludge (BS) batches from two factories with different operation modes were sampled and subjected to pyrolysis (P materials) and to pyrolysis followed by acid washing (PW materials). All the materials were characterized by proximate analysis, total organic carbon (TOC) and inorganic carbon (IC), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and N2 adsorption isotherms (specific surface area (SBET)and porosity determination). Sludge from the two factories proved to have distinct physicochemical properties, mainly in what concerns IC. After pyrolysis, the washing step was essential to reduce IC and to considerably increase SBET, yet with high impact in the final production yield. Among the materials here produced, PW materials from PS were those having the highest SBET values (387–488 m2 g−1). Overall, it was found that precursors from different factories might originate final materials with distinct characteristics, being essential to take into account this source of variability when considering paper mill sludge as a raw material. Nevertheless, for PS, low variability was found between batches, which points out to the reliability of such residues to be used as precursors of carbon adsorbents.

Impact of multiple wastewater feedings on the efficiency of nutrient removal in an IFAS-MBSBBR: number of feedings vs. efficiency of nutrient removal.

This article presents the results of research into the influence of one, two and three wastewater feedings in a cycle on efficiency and performance of combined biological nitrogen and phosphorus removal in an integrated fixed-film activated sludge and moving-bed sequencing batch biofilm reactor (IFAS-MBSBBR). The experiment lasted 158 days and was conducted in two laboratory models of the IFAS-MBSBBR with an active volume of 28 L. It was found that along with an increase in the number of wastewater feedings, an increase in nitrogen removal efficiency was observed (from 56.9 ± 2.30% for a single feeding to 91.4 ± 1.77% for three feedings). Moreover, the contribution of simultaneous nitrification/denitrification in nitrogen removal increased (from 2.58% for a single feeding to 69.5% for three feedings). Systems with a greater number of feedings stimulated the process of denitrifying phosphorus removal. Regardless of the way in which wastewater feeding was applied to the IFAS-MBSBBR, highly efficient chemical oxygen demand (COD) removal (94.8 ± 1.80%) and biological phosphorus removal (98.9 ± 0.87%) were achieved.

Activated Sludge and other Aerobic Suspended Culture Processes

This is a literature review for the year 2014 and contains information specifically associated with suspended growth processes including activated sludge and sequencing batch reactors. This review is a subsection of the treatment systems section of the annual literature review. The review encompasses modeling and kinetics, nutrient removal, system design and operation. Compared to past reviews, many topics show increase in activity in 2014. These include, nitrogen and phosphorus control, fate and effect of xenobiotics, industrial wastes treatment, and some new method for the determination of activated sludge. These topics are referred to the degradation of constituents in activated sludge. Other sections include population dynamics, process microbiology of activated sludge, modeling and kinetics. Many of the subsections in the industrial wastes: converting sewage sludge into fuel gases, thermos-alkali hydrolysis of Waste Activated Sludge (WAS), sludge used as H2 S adsorbents were also mentioned in this review.