Reduction Of Excess Sludge Production Research Articles

Reducing excess sludge volume in sequencing batch reactor by integrating ultrasonic waves and ozonation.

The effects of ultrasonic waves and ozonation on the reduction of produced sludge in the sequencing batch reactor (SBR) system were investigated in laboratory-scale experiments. For this purpose, the optimal ozone dosage was determined by measuring soluble chemical oxygen demand (SCOD), protein concentration, turbidity level, and biomass yield coefficient. Next, the effect of its integration with different levels of ultrasonic specific energy was evaluated. Based on the results, the minimum excess sludge production in the SBR system was achieved at the ozone dosage of 11mg O3/g MLSS followed by ultrasonic specific energy of 12000kJ/kg TS. In this case, the biomass yield coefficient decreased from 0.75 in the control reactor to 0.34mg MLSS/mg COD in the test reactor, which was equal to a 54% reduction in excess sludge production in the SBR system. In these circumstances, the removal efficiencies of COD, total nitrogen, and total phosphorus were measured as 90%, 82%, and 81%, respectively.

Reduction of excess sludge production by membrane bioreactor coupled with anoxic side-stream reactors

While cleaning wastewater, biological wastewater treatment processes such as membrane bioreactors (MBR) produce a significant amount of sludge that requires costly management. In the oxic-settling-anoxic (OSA) process, sludge is retained for a temporary period in side-stream reactors with low oxygen and substrate, and then it is recirculated to the main reactor. In this way, excess sludge production is reduced. We studied the influence of the rate of sludge exchange between MBR and side-stream anoxic reactors on sludge yield reduction within MBR. Two MBRs, namely, MBROSA and MBRcontrol, each coupled with separate external anoxic side-stream reactors, were run in parallel for 350 days. Unlike MBRcontrol, MBROSA had sludge exchange with the external reactors connected to it. During the investigation over a sludge interchange rate (SIR) range of 0–22%, an SIR of 11% achieved the highest sludge reduction (58%). Greater volatile solids destruction i.e., bacterial cell lysis and extracellular polymeric substance (EPS) destruction occurred at the SIR of 11%, which helped to achieve the highest sludge reduction. The enhanced volatile solids destruction was evident by the release of nutrients in the external anoxic reactors. It was confirmed that the sludge yield reduction was achieved without compromising the wastewater treatment quality, sludge settleability and hydraulic performance of the membrane in MBR.

Reduction of excess sludge production by microwave/activated carbon fibre pretreatment process based on lysis-cryptic growth

Reduction of excess sludge production by microwave/activated carbon fibre pretreatment process based on lysis-cryptic growth

Oxic settling anaerobic (OSA) process for excess sludge reduction: 16 months of management of a pilot plant fed with real wastewater

An OSA (oxic settling anaerobic) pilot plant, preliminarly ran as a conventional activated sludge (CAS) system, was managed under several operating conditions for 16 months. The aim was to evaluate the reduction of excess sludge production due to the recirculation of activated sludge trough the sludge holding tank (SHT). The sludge retention time varied from 37 to 406 days according to the excess sludge wastage. The oxidation/reduction potential (ORP) inside the sludge holding tank was of – 248 ± 133 mV. The observed sludge yield, obtained by feeding the system with real wastewater, varied from 0.112 to 0.465 gTSS/gCOD, with a reduction of the excess sludge production of 49.6 ± 20.7% compared to the CAS system. The recirculation of the sludge through the SHT favoured the COD and ammonia nitrogen solubilization connected to the sludge decay. The release of soluble phosphorus due to the phosphorus accumulating organisms metabolism was also noticed.

薬剤と微生物処理を併用したし尿汚泥の減量化技術の開発

新規に開発した汚泥減量化システムについて，し尿処理場への適用を検討した。本減量化システムは化学処理と微生物処理を組み合わせたもので，第1段階ではアルカリ処理によって減量化され，後段の微生物処理によってさらなる減量化が進行する。2か所のし尿処理場より採取した汚泥について，まずアルカリ回分処理により，その減量化特性を評価した。次に，微生物処理も組み合わせた連続処理を実施し，30～50 %の汚泥減量化率が得られた。この結果は，本技術のし尿処理場への適用可能性を示唆するものと考えられた。

Activated sludge mass reduction and biodegradability of the endogenous residues by digestion under different aerobic to anaerobic conditions: Comparison and modeling

This study was performed to identify suitable conditions for the in-situ reduction of excess sludge production by intercalated digesters in recycle-activated sludge (RAS) flow. The objective was to compare and model biological sludge mass reduction and the biodegradation of endogenous residues (XP) by digestion under hypoxic, aerobic, anaerobic, and five intermittent-aeration conditions. A mathematical model based on the heterotrophic endogenous decay constant (bH) and including the biodegradation of XP was used to fit the long-term data from the digesters to identify and estimate the parameters. Both the bH constant (0.02–0.05d−1) and the endogenous residue biodegradation constant (bP, 0.001–0.004d−1) were determined across the different mediums. The digesters with intermittent aeration cycles of 12h–12h and 5min–3h (ON/OFF) were the fastest, compared to the aerobic reactor. The study provides a basis for rating RAS-digester volumes to avoid the accumulation of XP in aeration tanks.

Reduction of excess sludge production in sequencing batch reactor (SBR) by lysis–cryptic growth using homogenization disruption

A lysis–cryptic growth system, which combined high-pressure-homogenization (HPH) for sludge disruption, was proposed to reduce excess sludge production in SBR. Experimental data was analyzed with the aid of response surface models to determine the optimal HPH disruption pressure, which was 70MPa. By combining a 5.4m3/d pilot SBR with HPH disruption, the new system achieved a 42.4% sludge reduction rate over a 75days operation. Based on measurement of oxygen uptake rate and activity of the dehydrogenase, the lysis–cryptic growth system resulted in negligible change of the sludge activity. However, an increase of 0.04mg/L of total-phosphorus (TP) and 2.40mg/L suspended-solids (SS) was observed in the effluent due to the process of lysis–cryptic growth. Except for above listed points, the new system demonstrated improved sludge reduction performance while the direct cost of pilot SBR lysis–cryptic growth was only 0.177US dollar per kilogram (dry sludge) according to estimation.

Optimization of ozonation process for the reduction of excess sludge production from activated sludge process of sago industry wastewater using central composite design.

Sago industries effluent containing large amounts of organic content produced excess sludge which is a serious problem in wastewater treatment. In this study ozonation has been employed for the reduction of excess sludge production in activated sludge process. Central composite design is used to study the effect of ozone treatment for the reduction of excess sludge production in sago effluent and to optimise the variables such as pH, ozonation time, and retention time. ANOVA showed that the coefficient determination value (R 2) of VSS and COD reduction were 0.9689 and 0.8838, respectively. VSS reduction (81%) was achieved at acidic pH 6.9, 12 minutes ozonation, and retention time of 10 days. COD reduction (87%) was achieved at acidic pH 6.7, 8 minutes of ozonation time, and retention time of 6 days. Low ozonation time and high retention time influence maximum sludge reduction, whereas low ozonation time with low retention time was effective for COD reduction.

Reduction of excess sludge production in sequencing batch reactor through incorporation of chlorine dioxide oxidation

In this study, chlorine dioxide (ClO 2) instead of chlorine (Cl 2) was proposed to minimize the formation of chlorine-based by-products and was incorporated into a sequencing batch reactor (SBR) for excess sludge reduction. The results showed that the sludge disintegrability of ClO 2 was excellent. The waste activated sludge at an initial concentration of 15 g MLSS/L was rapidly reduced by 36% using ClO 2 doses of 10 mg ClO 2/g dry sludge which was much lower than that obtained using Cl 2 based on similar sludge reduction efficiency. Maximum sludge disintegration was achieved at 10 mg ClO 2/g dry sludge for 40 min. ClO 2 oxidation can be successfully incorporated into a SBR for excess sludge reduction without significantly harming the bioreactor performance. The incorporation of ClO 2 oxidation resulted in a 58% reduction in excess sludge production, and the quality of the effluent was not significantly affected.

Evaluation of a new model for the reduction of excess sludge production by ozonation of return activated sludge: what solids COD fraction is affected?

This paper aims at clarifying the effect of ozone on the RAS solids to model activated sludge systems equipped with RAS-ozonation processes for the reduction of sludge production. A common hypothesis is that ozone only affects active biomass by promoting cryptic growth. Data from a pilot-scale study were used to test this and two other model extensions to IWA-ASM3. All model extensions were able to simulate the observed linear reduction in sludge production with increasing ozone dose when the MLVSS are kept constant. However, model simulations showed the inconsistency of the cryptic growth hypothesis with the extent of sludge reduction. The second tested model extensions assumes that ozone affects all the solids fractions (active biomass, endogenous residue, and influent inert particulate COD) equally. This extension could properly simulate the observed sludge reduction, but it failed to predict the trends in effluent BOD₅, ATP/VSS, and nitrification rates. A third tested model extension, which performed better, assumes that biomass is inactivated at a specific rate higher than the specific rate of transformation by ozone of the other solids fractions. Finally, the predictions from this model extension were most accurate if either (i) the nitrifiers were inactivated at a lower rate then heterotrophs, (ii) the nitrifiers model parameters (e.g., maximum growth rate) were changed under ozone (i.e., metabolic adaptation, (iii) or both.

Oxic-settling-anoxic (OSA) process combined with 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to reduce excess sludge production in the activated sludge system

The potential of oxic-settling-anoxic (OSA) process with addition of 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to reduce excess sludge production was investigated. TCS was dosed into aeration tank with 0.05, 0.10 and 0.15 g every other day in three lab-scale OSA processes, respectively to form the TCS and OSA combined processes. The OSA and TCS combined processes reduced sludge yield by 21–56% under the same sludge retention time (6.75 h) in sludge anoxic holding tank. Substrate removal capability, effluent NH 3-N concentrations and total phosphorus removal rates were not adversely affected by the presence of TCS or insertion of sludge anoxic holding tank, but total nitrogen removal rates only decreased significantly in the system with addition of 0.15 g TCS during the 60-day continuous operation. The settleability of sludge in four systems was qualitatively comparable and not significantly different. Microscopic examination and the banding patterns of DGGE profiles demonstrated that microbial population changed after TCS addition and insertion of anoxic sludge holding tank. The results suggest that TCS and OSA combined process is effective in reducing sludge yield, and process performance as well as sludge settleability are not significantly affected by introduction of the chemical uncoupler. The results imply that reduction of excess sludge production is due to uncoupled metabolism at low TCS dosage, but microbial death at high TCS dosage.

Effect of thermochemical sludge pretreatment on sludge reduction and on performances of anoxic‐aerobic membrane bioreactor treating low strength domestic wastewater

AbstractBACKGROUND: Reduction of excess sludge production has become an urgent issue. An investigation into the influence of thermochemical sludge pretreatment on sludge reduction in a bench‐scale anoxic‐aerobic membrane bioreactor was performed. Two systems were operated. In one system, part of the mixed liquid (1.5% of the influent flow rate) was pretreated thermochemically (at 80 °C, pH 11 and 3 h) and returned to the bioreactor. This study examined and evaluated the effect of thermochemical sludge pretreatment on the reduction of excess sludge and on the performance of the system.RESULTS: The average solubilization efficiency of the pretreated sludge was found to be about 0.2. The sludge production rate of the experimental system (E‐MBR) was less than that of the control (C‐MBR) by about 33%. The total phosphorus was removed mainly by normal cell synthesis, with removal efficiencies of 38–40% and 40–42% for the E‐MBR and C‐MBR, respectively. The total nitrogen removal in the E‐MBR was slightly higher than in the C‐MBR due to supply of soluble chemical oxygen demand (SCOD) from the digested sludge solution as an external carbon source. The mixed liquor volatile suspended solids (MLVSS) and mixed liquor suspended solids (MLSS) ratios for the two systems were almost identical, in the range 74–77%, indicating that the inorganics from the disintegrated cells do not accumulate as particulates in the reactor. The TMP was maintained at less than 6 cmHg for 180 days without membrane cleaning.CONCLUSION: Thermochemical sludge pretreatment can play an important role in reducing sludge production. The qualities of the effluent water were not significantly affected during 6 months of operation. Copyright © 2009 Society of Chemical Industry

Reduction in excess sludge production in a dairy wastewater treatment plant via nozzle-cavitation treatment: Case study of an on-farm wastewater treatment plant

Nozzle-cavitation treatment was used to reduce excess sludge production in a dairy wastewater treatment plant. During the 450-d pilot-scale membrane bioreactor (MBR) operation, when 300 l of the sludge mixed liquor (1/10 of the MBR volume) was disintegrated per day by the nozzle-cavitation treatment with the addition of sodium hydrate (final concentration: 0.01% W/W) and returned to the MBR, the amount of excess sludge produced was reduced by 80% compared with that when sludge was not disintegrated. On the basis of the efficiency of CODCr removal and the ammonia oxidation reaction, it was concluded that the nozzle-cavitation treatment did not have a negative impact on the performance of the MBR. The estimation of the inorganic material balance showed that when the mass of the excess sludge was decreased, the inorganic content of the activated sludge increased and some part of the inorganic material was simultaneously solubilized in the effluent.

Chemical Oxygen Demand and the Mechanism of Excess Sludge Reduction in an Oxic-Settling-Anaerobic Activated Sludge Process

A modified activated sludge process, called the oxic-settling-anaerobic (OSA) process, achieved effective reduction in excess sludge production. Its key feature is the insertion of a sludge holding tank in the sludge return circuit to provide an anaerobic sludge zone. Our previous studies suggested that such excess sludge reduction might be associated with an increased sludge decay rate and the effective consumption of organic substrates generated during the retention of the thickened sludge in the sludge holding tank under a low oxidation-reduction potential (ORP) at −250 mV . To confirm this suggestion, we analyzed the chemical oxygen demand (COD) balance in the sludge holding tank through batch experiments to simulate the sludge concentration, ORP level, and retention time in the sludge holding tank. The COD generated from the sludge reduction in the tank was utilized by organic gas (mainly CH4 ) production, denitrification, sulfate reduction, and phosphorus release, among which the gas production acco...

Structural Analysis and Dewatering Characteristics of Waste Sludge from WWTP MBR

A pilot‐scale UF membrane bioreactor (MBR) of 1 m3/day capacity was set up in an industrial wastewater treatment plant to evaluate its performance. This study mainly focused on testing the dewaterability and structural analysis of MBR sludge. MBR had 14% reduction of excess sludge production in relative to the conventional activated sludge process (CAS sludge). For dewatering, MBR sludge had comparable dewaterability with the CAS sludge but required nearly 20% less flocculant to reach the highest filterability χ and lowest specific filtration resistance (SRF). This could reduce the cost for running the dewatering facilities and final disposal. Meanwhile the chemical and morphological analyses on MBR sludge exhibited lower EPS (exocellular polymeric substances) content, slightly smaller flocs and more compact morphology. Additionally, to estimate the appropriate polyelectrolyte dose prior to dewatering, we measured the hysteresis loop area of the sludge rheogram (shear stress vs. shear rate) using a co‐axial cylinder viscometer. For both sludges, the area dramatically increased at some critical flocculant dosage and then plateaued off. The critical dosage, though not optimal, still led to an acceptable dewatering performance for the sludge.

Comparison between inhibitor and uncoupler for minimizing excess sludge production of an activated sludge process

In order to study the minimization of excess sludge production, the reduction in the excess sludge production in the presence of an inhibitor and uncoupler was studied in this work. The experimental results show that such an addition could effectively reduce the production of excess sludge. With the energy uncoupling model established in this work, energy uncoupling coefficient (E u) was used to evaluate the reduction in excess sludge production. The energy uncoupling coefficients in the presence of dinitrophenol (dNP), Zn2+, and Cu2+ was 0.75, 0.46, and 0.18, respectively. The analysis demonstrated that energy spilling occurred in the presence of dNP, and that dNP was an effective uncoupler for reducing the production of excess activated sludge without affecting the microbial respiration activity.

Reduction of excess sludge production using mechanical disintegration devices

The usability of mechanical disintegration techniques for the reduction of excess sludge production in the activated sludge process was investigated. Using three different disintegration devices (ultrasonic homogeniser, stirred media mill, high pressure homogeniser) and different operational parameters of the disintegration, the effect of mechanical disintegration on the excess sludge production and on the effluent quality was studied within a continuously operated, laboratory scale wastewater treatment system with pre-denitrification. Depending on the operational conditions and the disintegration device used, a reduction of excess sludge production of up to 70% was achieved. A combination of mechanical disintegration with a membrane bioreactor process with high sludge age is more energy effective concerning reduction of sludge production than with a conventional activated sludge process at lower sludge ages. Depending on the disintegration parameters, the disintegration has no, or only minor, negative effect on the soluble effluent COD and on the COD-removal capacity of the activated sludge process. Nitrogen-removal was slightly deteriorated by the disintegration, whereas the system used was not optimised for nitrogen removal before disintegration was implemented.

Biological sludge solubilisation for reduction of excess sludge production in wastewater treatment process

A novel sludge disintegration system (JFE-SD system) was developed for the reduction of excess sludge production in wastewater treatment plants. Chemical and biological treatments were applied to disintegrate excess sludge. At the first step, to enhance biological disintegration, the sludge was pretreated with alkali. At the second step, the sludge was disintegrated by biological treatment. Many kinds of sludge degrading microorganisms integrated the sludge. The efficiency of the new sludge disintegration system was confirmed in a full-scale experiment. The JFE-SD system reduced excess sludge production by approximately 50% during the experimental period. The quality of effluent was kept at quite a good level. Economic analysis revealed that this system could significantly decrease the excess sludge treatment cost.

Organic matter release in low temperature thermal treatment of biological sludge for reduction of excess sludge production

Thermal treatment applied in association with a biological system allows for a significant reduction in excess sludge production (approximately 50%). In general, heat treatment is described as a sludge disintegration technique. This paper offers a thorough study on the impact of heat treatment, at temperatures below 100 degrees C, on the solubilisation of the sludge COD and its biodegradability. Discontinuous heating experiments were performed on activated and digested sludge. At all temperatures tested the released COD for digested sludge was systematically higher than that for activated sludge (15 and 40%, respectively, at 95 degrees C for 40 min of contact time). For the first 30 min, a 1st order kinetic, with respect to the residual COD, was systematically found. In the range of 40-95 degrees C, digested sludge had a lower activation energy than activated sludge (26 kcal/mol compared to 70-160 kcal/mol). COD solubilisation is thus more positively influenced by temperature in the case of activated sludge. This may be due to the significant difference in the ratio of protein/carbohydrate in digested and activated sludge (1-5 and 0.2-0.7, respectively). The increase in the COD/TKN ratio in the solubilised fraction after thermal treatment of activated sludge suggests a preferential solubilisation of proteins over carbohydrates. Respirometric tests performed on the solubilised COD showed that whatever the sludge origin, only 40-50% of released COD is biodegradable at a conventional hydraulic retention time (i.e., 24 h). Hence, heat treatment would act more through organic matter solubilisation rather than by a biodegradability increase.

Technical and Economical Evaluation of a Thermal, and Two Oxidative Techniques for the Reduction of Excess Sludge Production

Municipal wastewater treatment is closely linked with the production of sludge. This production may be reduced by combining a sludge disintegration technique with a conventional biological reactor, such as an activated sludge. The disintegration techniques are based on mechanical, electrical, thermal, thermo-chemical, biological and oxidative treatments. This work tries to give an evaluation of the efficiency and the economics of disintegration techniques that have demonstrated their potential to reduce the excess sludge production when combined to an activated sludge plant fed with a real urban wastewater. A high ESP reduction rate is achievable (more than 40%) by using disintegration technique such as a thermal (95°C), an ozonation or a hydrogen peroxide treatment. These three disintegration techniques were studied in details in our laboratories. The experiments carried out provided the technical data in order to make an assessment of the economics of the three selected combined processes. The ozone appeared to be the most interesting route for sludge reduction but the heating route is also economically competitive with conventional sludge treatment and disposal especially if stringent constraints on the sanitary quality of the sludge are imposed.