Characterization of sludges for predicting anaerobic digester performance.

Batch anaerobic digestion tests of primary sludge and waste activated sludge were conducted for a duration of 123 days to determine the ultimate degradability of the sludges. For primary sludges the inert fraction of the particulate COD that was predicted by the wastewater models could be employed to predict their biodegradability under anaerobic conditions. The degradation of waste activated sludge was adequately characterized for the first 60 days of digestion using a model that assumed equivalent biodegradability of particulate COD components under aerobic and anaerobic conditions. However after 60 days of anaerobic digestion it appeared that decay of the endogenous products was occurring. This could be described with a first order decay function with a coefficient of 0.0075 d(-1). For continuous flow digesters operating at SRTs of 30-60 days, the predicted VSS destruction with the modified model was approximately 10% higher than that predicted on the basis of inert endogenous decay products.     

Application of the flotation process to thicken the sludge from a DAF plant.

Dissolved air flotation (DAF) was evaluated for thickening of the sludges from a water treatment plant which uses DAF. Solid flux theory for gravity thickening was applied to the solid flux of DAF sludge. The higher the polymer dosage, at fixed solid concentration, the greater the rising velocity becomes. When applied with solid flux equations, a similar relationship to that of gravity thickening has been found. However, the values were much higher than in gravity thickening, because both the inflow solid concentration and the floating velocity were higher than for settled sludge. With this result, the proper dosage of polymer could be derived from the relationship between total solid flux and withdrawal velocity of DAF sludge.     

Comparison of different thickening methods for active biomass recycle for anaerobic digestion of wastewater sludge

The effect of returning solids to the digester, after one of three thickening processes, on volatile solids reduction (VSR) and gas production was investigated. Three different thickening methods were compared: centrifugation, flotation and gravitational sedimentation. The amount and activity of retained biomass in thickened recycled sludge affected the efficiency of digestion. Semi-continuous laboratory digesters were used to study the influence of thickening processes on thermophilic sludge digestion efficiency. Centrifugation was the most effective method used and caused an increase of VSR from 43% (control) up to 70% and gas generation from 0.40 to 0.44 L g(-1) VS. Flotation and gravitational sedimentation ways of thickening appeared to be less effective if compared with centrifugation. These methods increased VSR only by up to 65 and 51%, respectively and showed no significant increase of gas production. The dewatering capacity of digested sludge, as measured by its specific resistance to filtration, was essentially better for the sludge digested in the reactors with centrifugated and settled recycle. The VS concentration of recycle (g L(-1)), as reflecting the amount of retained biomass, appeared to be one of the most important factors influencing the efficiency of sludge digestion in the recycling technology.     

Comparison of extracellular polymeric substances (EPS) extraction from two different activated sludges

The characteristics of extracellular polymeric substances (EPS) extracted with five different extraction protocols from two different activated sludges were studied. The results showed that the major EPS constituent extracted by centrifugation was protein for the sludge in sequencing batch reactor treating chemical wastewater, and nucleic acid for the sludge in moving bed biofilm reactor treating synthetic urban wastewater. The order of EPS extraction amounting from the two sludges was formaldehyde + NaOH > formaldehyde + heating > EDTA > heating > centrifugation. The different extraction methods, the wastewater type, and activated sludge source greatly affected the amount and composition of EPS. The chemical extracted methods were more effective than the physical methods in extracting EPS for the two sludges. Moreover, formaldehyde combined NaOH was most effective in extracting EPS for the two sludges. However, chemical extraction could contaminate the EPS solution, which was pointed out by infra-red analysis and was also proved by cell lyses during EPS extraction and carrying over of the chemical extractant. Therefore, this study highlights that the choice of EPS extraction method should consider both the extraction yield and content and the contamination of extracting reagents to the EPS solution. The extraction procedures should be optimized and most effective.     

Sludge-sludge interaction in the enhanced biological phosphorus removal process.

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic-aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.     

Application of metaproteomic analysis for studying extracellular polymeric substances (EPS) in activated sludge flocs and their fate in sludge digestion

Metaproteomic analysis, comprising protein separation and identification, was applied to study extracellular proteins in activated sludges and to track their fate in sludge digestion under both anaerobic and aerobic conditions. The complex sludge proteins were first separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and further analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS) to search their identification. Base extraction and cation exchange resin (CER) method were used to extract EPS from sludges at 0, 12 and 30 days of batch digestion. Several important observations were made during this study. Firstly, protein bands were well separated by extraction/SDS-PAGE protocol used in this study. Secondly, numerous protein bands remained after digestion, indicating that these proteins are not easily degradable in sludge digestion. Thirdly, protein bands detected following anaerobic and aerobic digestion differed, suggesting that proteins degraded in two different digestion environments are not the same. Finally, protein bands that emerged distinctively following anaerobic digestion was found to be subunits of methyl-coenzyme M reductase, the enzyme involved in methane generation, in Methanosarcina barkeri. These results demonstrated that metaproteomic investigation on activated sludge EPS is useful for studying floc formation in activated sludges and their degradation in various digestion environments.     

Towards exposure of elusive metabolic mixed-culture processes: the application of metaproteomic analyses to activated sludge.

Protein expression is a direct reflection of specific microbial activities in any ecosystem. In order to assess protein expression in mixed microbial communities, the feasibility of applying proteomic techniques to activated sludge samples has recently been demonstrated. We report the application of metaproteomics to two activated sludges from a laboratory-scale sequencing batch reactor with dissimilar phosphorus removal performances. Fluorescence in situ hybridization (FISH) revealed that the sludge with good enhanced biological phosphorus removal performance (EBPR) was dominated by Betaproteobacteria (65% of EUBMIX binding cells) and gave positive signals for the Rhodocyclus-type PAO specific probe (59%). The non-EBPR sludge was dominated by tetrad-forming Alphaproteobacteria (75%). With regard to the proteomic investigation, 630 individual protein spots were matched across the replicate groups of the anaerobic and aerobic phases of the EBPR sludge with 9.4% of all spots being statistically different between the two phases. The non-EBPR metaproteomic maps exhibited 590 matched spots with 14.7% statistical differences between the two phases. Overall, the non-EBPR sludge expressed around 30% more significant differences than the EBPR sludge. The comparison of protein expression in the two sludges showed that their metaproteomes were substantially different and this was reflected in their microbial community structures and metabolic transformations.     

Co-conditioning and dewatering of alum sludge and waste activated sludge.

Co-conditioning and dewatering behaviors of alum sludge and waste activated sludge were investigated. Two different sludges were mixed at various ratios (2:1; 1:1; 1:2; 1:4) for study. Capillary suction time (CST) and specific resistance to filtration (SRF) were utilized to assess sludge dewaterability. Relatively speaking, waste activated sludge, though of higher solid content, was more difficult to be dewatered than alum sludge. It was found that sludge dewaterability and settlability became better with increasing fraction of alum sludge in the mixed sludge. Dosage required of the cationic polyelectrolyte (KP-201C) for dewatering was reduced as well. It is proposed that alum sludge acts as skeleton builder in the mixed sludge, and renders the mixed sludge more incompressible which is beneficial for sludge dewatering. Implications of the results of the study to the sludge management plan for Taipei City that generates both alum sludge and waste activated sludge at significant amount are also discussed. The current sludge treatment and disposal plan in Metropolitan Taipei could be made more cost-effective.     

Initial examination of microwave pretreatment on primary, secondary and mixed sludges before and after anaerobic digestion.

The effects of microwave pretreatment on disintegration and mesophilic digestion of waste activated sludge (WAS), primary sludge (PS), combined (PS + WAS) sequencing batch reactor (SBR) sludge and anaerobically digested biocake were investigated by both household and bench scale industrial types microwaves at temperatures below and above boiling point. Pretreatment variables, temperature, intensity (cooking rate) and sludge concentration had statistically significant effects on solubilization. The microwave pretreatment also increased the bioavailability of sludge components under batch anaerobic digestion and enhanced the dewaterability of pretreated sludges after digestion. However, the level of improvements in solubilization and biodegradation from different waste sludges were different. While the largest improvement in ultimate biodegradation was observed in WAS, microwave irradiation only affected the rate of biodegradation of pretreated PS samples. Similarly, relatively lower solubilization ratios achieved for combined - SBR sludge was attributed to high sludge age of extended aeration SBR unit. It is possible that initial sludge characteristics may influence final pretreatment outcomes so that general statements of performance cannot always be made.     

A comparison of ultrasound treatment on primary and secondary sludges.

Ultrasound treatment of primary and secondary sludges was conducted to improve the qualities of sludges for the anaerobic digestion. The impacts of different sonication times, sonication densities and solids concentrations on ultrasonication efficiency were examined. The experimental results indicated that the significant reduction in particle size and increase in soluble organics could be achieved, implying that ultrasonication could offer a feasible treatment method to efficiently disintegrate sludge. The greater decrease in particle size and increase in soluble organics of sludge indicated that the secondary sludge has a more remarkable improvement after sonication over the primary sludge. With respects to the extent of disintegration and energy consumption, higher sonication density performed more effectively in terms of specific energy. There exists an optimal solids concentration range for both the sludges for optimum sonication. Within the optimal solids concentration range, efficient sonication can be effected and sludge would be disintegrated efficiently. The ultrasound would be attenuated by scattering and absorption if the solids concentration exceeds the optimal range. It appeared from the study that the mechanical shear forces caused by ultrasonic cavitation could be a key factor for sludge disintegration and collapse of cavitation bubbles could significantly alter the sludge characteristics.     

Evaluation, selection and initial performance of a large scale centralised biosolids facility at Oxley Creek Water Reclamation Plant, Brisbane.

Recent upgrades to Brisbane City Council's Water Reclamation Plants (WRP) for improved nutrient removal has led to a significant increase in sludge production, and loss in potential anaerobic degradability. This increase in sludge production brought forth an economic driver for an improved, integrated biosolids handling strategy. The solution adopted by Brisbane Water, was a centralised thermal hydrolysis facility at Oxley Creek WRP to process the waste activated sludges generated at a total of five WRPs in the region. The thermal hydrolysis process uses high temperature and pressure to make non-degradable material more readily digestible by anaerobic bacteria and hence achieve greater efficiency in the overall anaerobic digestion process. Dewaterability is also improved, as the thermal hydrolysis process releases some of the bound water from the waste activated sludge. The viability of this solution is linked primarily to the reduction in mass and volume of biosolids which leads to lower transportation and disposal costs. After four months of operation, the Oxley Creek thermal hydrolysis plant has resulted in a 70% reduction in biosolids quantities (bulk volume) and disposal costs. The process is currently being optimised. Savings to date have reached about AUD 80,000 per month. Technical and operational issues which emerged during commissioning are also described.     

Pilot study of a fluidized-pellet-bed technique for simultaneous solid/liquid separation and sludge thickening in a sewage treatment plant.

A fluidized-pellet-bed separator with movable sludge hoppers was applied in pilot scale for the separation and thickening of activated sludge mixture liquid. Under the condition of suspension SS around 4,000 mg/L, polymer (CJX103, cationic, MW 5 x 10(6)) dose at a dry solid ratio of 0.003 and upward flow rate at 5.4 m/hr, the fluidized pellet bed performed solid/liquid separation and sludge thickening well. The SS concentration of the treated water was about 5 mg/L on average and the moisture content of the sludge after screening for 5 min was less than 94%, which is much lower than that after conventional settling and thickening and easy to be finally disposed. At a higher upward flow rate of 7.2 m/hr, similar results could also be obtained but higher polymer dose (solid ratio of 0.004) was required. The morphological characteristics and density-size relationship of the granular particles formed in the fluidized pellet bed were also investigated by image analysis and settling velocity measurement of individual particles. The two-dimensional fractal dimension was evaluated to be 1.6-1.8, showing a good quasi-spherical morphology of the granular particles with their density much higher than the conventional flocs. The results of the pilot study indicate a possible way to innovate the conventional secondary settling and gravitational thickening processes for solid/liquid separation and sludge handling, especially for small scale wastewater treatment plants to reach the goal of space saving and higher treatment efficiency.     

Ultrasonic sludge treatment for enhanced anaerobic digestion.

Ultrasound is the term used to describe sound energy at frequencies above 20 kHz. High-powered ultrasound can be applied to a waste stream via purpose-designed tools in order to induce cavitation. This effect results in the rupture of cellular material and reduction of particle size in the waste stream, making the cells more amenable to downstream processing. sonix is a new technology utilising high-powered, concentrated ultrasound for conditioning sludges prior to further treatment. This paper presents recent results from a number of demonstration and full-scale plants treating thickened waste activated sludge (TWAS) prior to anaerobic digestion, therefore enhancing the process. The present studies have proved that the use of ultrasound to enhance anaerobic digestion can be achieved at full scale and effectively result in the TWAS (typically difficult to digest) behaving, after sonication, as if it were a "primary" sludge. The technology presents benefits in terms of increased biogas production, better solids reduction, improved dewatering characteristics of the digested sludge mixture and relatively short payback periods of two years or less subject to the site conditions and practices applicable at that time.     

Full scale implementation of the nutrient limited BAS process at S?dra Cell V?r?.

A combination of the suspended carrier biofilm process and the activated sludge process (biofilm-activated sludge--BAS) has been shown to be very successful for the treatment of different types of pulp and paper mill effluents. The robust biofilm pre-treatment in combination with activated sludge results in a stable, compact and highly efficient process. Recent findings have shown that nutrient limited operation of the biofilm process greatly improves the sludge characteristics in the following activated sludge stage, while minimising sludge production and effluent discharge of nutrients. The nutrient limited BAS process was implemented at full scale at the S?dra Cell V?r? kraft mill and taken into operation in July 2002. After start-up and optimisation over about 5 months, the process meets all effluent discharge limits. The removal of COD is close to 70% and the removal of EDTA greater than 90%. Typical effluent concentrations of suspended solids and nutrients during stable operations have been 20-30 mg/L TSS, 0.3-0.5 mg/L phosphorus and 3-5 mg/L nitrogen. The sludge production was 0.09 kgSS/kg COD removed and the sludge volume index was 50-100 mL/g.     

Anammox brings WWTP closer to energy autarky due to increased biogas production and reduced aeration energy for N-removal.

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2-3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15-20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.     

Anaerobic processes in activated sludge

We found anoxic zones in aerated activated sludge flocs, and demonstrated denitrification under normal operating conditions. Sulfate reduction was not found. Micro-environments and microbial conversions in flocs from bulking and non-bulking activated sludge were determined with microsensors for H₂S, O₂, NO₂₋ and NO₃₋. Denitriftcation and sulfate reduction rates were measured with ¹⁵N- and ³⁵S-tracer techniques. We showed that under normal reactor conditions (ca. 20% air saturation) anoxic zones develop within flocs allowing denitrification. The denitrtftcation rates amounted to 40% of the rates under anoxic conditions. At 100% air saturation no anoxic zones were found and no denitrification occurred. However, in flocs from bulking sludge (at 20% air saturation) anoxic zones were absent and denitrification did not occur. In bulking sludge only at total anoxia was denitrification found. Confocal microscopy showed that flocs from bulking sludge were much looser than those from non-bulking sludge. The absence of anoxic zones and of denitrification was attributed to the open floc structure, allowing advective oxygen transport.Sulfate reduction was not detected in any of the sludges tested by microsensors or by tracer techniques even under anoxic conditions. This indicates that the sulfur cycle (sulfate reduction and sulfide oxidation) does not play a role in mineralization processes and bulking in activated sludge. Preliminary molecular work (in situ hybridization with the 16S-rRNA probe SRB385) indicated the presence of small amounts of sulfate reducing bacteria in all sludges. Either the probe is not specific or the sulfate reducers present are not active under reactor conditions.     

Agricultural use of municipal wastewater sludges: phosphorus availability of biological excess phosphorus removal sludges.

Reuse of sewage sludges as phosphorus fertiliser requires the estimation of the plant availabilities of phosphorus (P) from different sludges. This study investigates the effect of lime stabilisation on the phosphorus availability from biological phosphorus removal sludges. In the first part of the study, pot experiments were carried out to assess the fertilising effect of a dewatered biological phosphorus removal sludge. Availability of P was determined in terms of plant-uptake. In the second part of the study, incubation tests were carried out to observe the change in the available P with time when the waste activated sludge (WAS) from an enhanced biological phosphorus removal (EBPR) process is mixed with the same soil. In this part, the plant available P was measured in terms of Olsen extractable P. A P-deficient, alkaline soil was used in the experiments and Lollium Perenne was selected as the testing plant. The results of the pot experiments revealed that lime-stabilisation of the sludge considerably decreased or retarded the availability of P in the sludge. In the incubation tests, the availability of phosphorus in the lime stabilised and nonstabilised sludge amended soil samples was close to each other. In general, P-availability was increased due to the sludge application except for the lime-stabilised dewatered sludge.     

林可霉素高浓度有机废水处理技术

采用厌氧颗粒和好氧活性污泥分别对内循环厌氧反应器(IC)和间歇式活性污泥法(SBR)进行污泥接种培养,研究水解酸化-IC-SBR工艺在林可霉素生产废水处理方面的运行效果。结果表明:在进水COD的质量浓度为6 000~9 000 mg/L,IC和SBR反应器中有机负荷分别为0.82 kg/(kg.d)和0.26 kg/(kg.d)左右的情况下,IC和SBR反应器分别运行60 d和7 d,COD平均去除率分别达到91%和61%,出水COD的质量浓度在300 mg/L以下,达到GB 8978—1996《污水综合排放标准》二级标准。     

Molecular biological methods to detect “Microthrix parvicella” and to determine its abundance in activated sludge

Molecular biological methods were evaluated in attempts to detect and quantitate levels of “Microthrix parvicella” in activated sludges. Approximately 66% of the 23S rRNA gene sequence of a strain (Ben43) of the Gram positive bulking and foaming organism “Microthrix parvicella” was determined, while a lesser amount was determined for “M. parvicella” strain RNI. The high mo1%G+C Gram positive bacteria (HGCGPBs) possess two powerfully diagnostic regions in the 23S rDNA and these were investigated in both strains. Firstly, the 18 nucleotide HGCGPB probe sequence (HGC69a) varied in at least two nucleotides with the sequence from both strains of “M. parvicella”. Secondly, an approximately 100 nucleotide stable insert between helices 54 and 55 in the 23S rRNA of HGCGPBs was discovered to be present in “M. parvicella”, but in both strains it was unique in length (79 nucleotides) and sequence. The region of the 23S rDNA with the stable insert was exploited to develop a polymerase chain reaction assay in which amplicons from “M. parvicella” were larger than those from nonHGCGPBs (i.e. all Bacteria except the HGCGPBs), and smaller than those from HGCGPBs. This assay was evaluated with DNAs extracted from activated sludges but although “M. parvicella” was morphologically identified, and was a dominant filament in at least one of the samples, no “M. parvicella” specific sized amplicons could be recovered from it. Amplicons of sizes generated by nonHGCGPBs and HGCGPBs were routinely produced in the stable insert PCR with DNAs from activated sludges where the highest yield was of amplicons from nonHGCGPBS.A second series of experiments were undertaken with the objective of evaluating the use of a non-radioactive hybridization method, based on extraction of bacterial RNA, for quantifying “M. parvicella” in activated sludge samples. Total nucleic acids were extracted from activated sludge samples and immobilized on nylon membranes. Probing with 16S rRNA-directed DIG-labelled oligonucleotide probes, detection of chemiluminescent signals on membranes and densitometry allowed hybridization signals to be quantified. The relationship between the amount of nucleic acid hybridized and the hybridization signal intensity observed was found to be linear over a specified range of signal intensities. A range of activated sludge samples were analysed for “M. parvicella” and variations in levels could be distinguished.     

Performance of high-rate sludge digesters fed with sonicated sludge.

A major limitation of anaerobic sludge digestion is the long hydraulic retention time (HRT) required for satisfactory stabilization which results in large digester size. This study explored a possibility of operating digesters at shortened HRTs by sonication pretreatment of secondary sludges. Four identical digesters designated D1, D2, D3 and D4 were fed with untreated and sludge sonicated at densities of 0.18 W/ml, 0.33 W/ml and 0.52 W/ml, respectively. All digesters were operated at three HRTs of 8-day, 4-day and 2-day. Comparing with the control digester (D1), total solids removal efficiencies improved by 12-19%, 17-36% and 20-39% in digesters D2, D3 and D4, respectively. The volatile solids removal was also increased by 11-21%, 17-33% and 19-36% in the respective digesters. The improved solids degradation corresponded with increase in biogas production by 1.4-2.5, 1.9-3.0 and 1.6-3.1 times, respectively. Increase in methane composition by 2-17% was also noted in all digesters fed with sonicated sludge. An analysis indicated that sonication pretreatment could enhance degradation of carbon, nitrogen and sulfur substances in the digestion. The study suggested that sonication of sludge is a possible pretreatment to shorten the digester operating HRT with improvement in solids degradation, biogas production and methane content. It can be deduced that to maintain a consistent solids loading at a desire performance, sludge digester with smaller size can be designed.