Volatile Suspended Solids Reduction Research Articles

Effect of temperature phased biological hydrolysis treatment on solubilization of wasted activated sludge

In this study, batch temperature-phased biological hydrolysis (TPBH) with conditions of biological hydrolysis (BH) at 42 °C for 1.5 days, followed by BH at 55 °C for 4.5 days were conducted to explore the solubilization behavior of wasted activated sludge (WAS) with the actions of endogenous enzymes produced by bacteria affiliated with WAS microbial community. The TPBH treatment resulted in 36.6% reduction in volatile suspended solids (VSS) with 91% of that achieved in the first three days of the treatment. Over the 6 days of TPBH treatment, the soluble chemical oxygen demand (SCOD), volatile fatty acids (VFA), and soluble microbial products (SMP) increased from 60 to 2665.0 mg/L, below 50 to 1309.0 mg/L, and 52.3 to 1042.6 mg/L, respectively, with 77.5% of SCOD, 74.9% of VFA, and 83.3% of SMP produced within 3 days of TPBH treatment. The experimental results and principal component analysis revealed that hydrolysis of extracellular proteins made a major contribution to the SCOD and VFA production. The Illumina sequencing analysis demonstrated that aerobic, facultative, and anaerobic organisms were co-existed in the WAS and BH treatment sludge, indicating that no drastic shift in the dominant bacteria groups occurred over the BH treatment period. Based on the results obtained in this study, we proposed a conceptual model for WAS BH treatment, which emphasizes the BH of WAS is a process to transform WAS biomass from the aerobic sludge microbial community to the anaerobic sludge community under the actions of endogenous enzymes produced by fermenting bacteria.

Linkage among the combined temperature–retention time condition, microbial interaction, community structure, and process performance in the hydrolysis of waste activated sludge

Numerous studies have revealed the effect of temperature and hydraulic retention time (HRT) on microbiota in sludge biological hydrolysis (BH). However, few scholars have explored the combined effect of these two critical BH parameters. This study explored the BH performance and community structures over 12 combined temperatures–HRT conditions for temperatures from 35 °C to 55 °C and HRTs from 1.5 days to 6.0 days. Results showed that the 12 combined conditions formed only six distinct community structures with each of them relating to a distinctive range of volatile suspended solid reduction rates. The nonmetric multidimensional scaling and species–species association analysis on the DNA sequencing data revealed that the community structure was greatly driven by the microbial interactions (e.g., heterogeneous commensalism and competition) under the effect of temperature and HRT. This study established the linkages among the combined BH temperature–HRT conditions, microbial interaction, microbial community, and BH performance.

An evaluation of lysozyme enzyme and thermal pretreatments on dairy sludge digestion and gas production.

Anaerobic digestion is one of the common methods of managing and stabilizing sludge. However, due to the limitations of the biological sludge hydrolysis stage, anaerobic decomposition is slow and requires a long time. This study evaluated the effects of thermal (80 °C) (TH-PRE) and a combination of thermal with the lysozyme enzyme (LTH-PRE) pretreatments on the enhancement of anaerobic activated sludge digestion. Response surface methodology was implemented to optimize enzyme pretreatment conditions (enzyme and mixed liquid suspended solids concentration). The results showed that both pretreatment methods increase soluble chemical oxygen demand (COD) and reduces total and volatile suspended solids (VSS), and phosphate concentration. The COD removal rate in LTH-PRE and TH-PRE was 95% and 81%, respectively. The value of VSS reduction in LTH-PRE and TH-PRE was 41% and 31%, more than the control operation, respectively. The biogas production in LTH-PRE and in TH-PRE also increased by 124% and 96%, respectively.

Enhancement of Hydrolysis and Biogas Production of Primary Sludge by Use of Mixtures of Protease and Lipase

This study aims to improve the hydrolysis and degradation of primary sludge by using wild-type enzymes (protease and lipase) and establishing the optimal enzymatic cocktail ratio. Primary sludge from three wastewater treatment plants (WWTPs) in Korea (Ulsan, Pohang, and Busan) were subjected to enzymatic hydrolysis. Protease and lipase were isolated from enzyme-producing microorganisms cultured from secondary sludge collected at 8 different digester sites in Korea. Primary sludge degradation through enzymatic hydrolysis was monitored by measuring the reduction in the volatile suspended solids (VSS) content of the sludge and enzyme cocktail mix for 72 h at 40oC and pH 7.0. The enzymatic cocktail of Ulsan primary sludge treated with protease to lipase at a ratio of 1:3 was found to be optimal at 33.3% VSS reduction. Biochemical methane potential (BMP) tests were employed to the optimal enzyme cocktail to measure the potential of the hydrolyzed substrate for further degradation (VSS reduction) and bioconversion to biogas using 125 mL serum bottles as anaerobic reactors for 30 days. BMP tests showed that there was an increase in biogas production by 84.1%, methane production by 89.8%, and methane yield by 9.6%. Methane production rate was also increased. The significant VSS concentration reduction and higher biogas and methane yield of the enzyme-treated primary sludge correlate to the fact that the complex polymeric organic materials were degraded leading to efficient utilization by the microorganisms in the anaerobic digestion process.

Effects of low-dosage ozone pre-treatment on the anaerobic digestion of secondary and mixed sludge.

The present study investigated the effects of ozonation pre-treatment at low-ozone dosage (below 100 mgO3/gTS0) with respect to previous studies, on the anaerobic digestion of waste-activated sludge alone and a mixture of activated sludge and primary sludge. Methane production and volatile suspended solids reduction efficiency were determined for different specific ozone dosages and compared with the values obtained in the absence of pre-treatment. Among the dosages tested in the study (from 4.8 to 73.2 mgO3/gTS0 for mixed sludge and from 3.5 to 53.6 mgO3/gTS0 for waste-activated sludge), the best results were obtained at the lowest ones: 4.8 and 3.5 mgO3/gTS0 for mixed sludge and waste-activated sludge, respectively. Indeed, at this dosage, an additional methane production of about 6% and 30% was achieved for mixed and waste-activated sludge, respectively; furthermore, the maximum CH4 production rate increased of about 21% and 33% for mixed and waste-activated sludge, respectively. With respect to the Gompertz model, the modified logistic model provided the best agreement to the experimental data of the specific methane yield production. The present study demonstrated the importance of investigating the application of low dosages when ozonation is being evaluated as a pre-treatment to enhance anaerobic digestion performance.

Evaluation of Feasibility of Using the Bacteriophage T4 Lysozyme to Improve the Hydrolysis and Biochemical Methane Potential of Secondary Sludge

Anaerobic digestion (AD) of secondary sludge is a rate-limiting step due to the bacterial cell wall. In this study, experiments were performed to characterize secondary sludges from three wastewater treatment plants (WWTPs), and to investigate the feasibility of using bacteriophage lysozymes to speed up AD by accelerating the degradation of bacterial cell walls. Protein was the main organic material (67.7% of volatile solids in the sludge). The bacteriophage T4 lysozyme (T4L) was tested for hydrolysis and biochemical methane potential. Variations in the volatile suspended solid (VSS) concentration and biogas production were monitored. The VSS reduction efficiencies by hydrolysis using T4L for 72 h increased and ranged from 17.8% to 26.4%. Biogas production using T4L treated sludges increased and biogas production was increased by as much as 82.4%. Biogas production rate also increased, and the average reaction rate coefficient of first-order kinetics was 0.56 ± 0.02/d, which was up to 47.5% higher compared to the untreated samples at the maximum. Alphaproteobacteria, Betaproteobacteria, Flavobacteriia, Gammaproteobacteria, and Sphingobacteriia were major microbial classes in all sludges. The interpretation of the microbial community structure indicated that T4L treatment is likely to increase the rate of cell wall digestion.

Temperature-Phased Biological Hydrolysis and Thermal Hydrolysis Pretreatment for Anaerobic Digestion Performance Enhancement

Thermal hydrolysis (TH) and biological hydrolysis (BH) are two main and growing anaerobic digestion pretreatment technologies. In this study, municipal wastewater sludge samples were collected from the Guelph Wastewater Treatment Plant (WWTP) in Ontario, Canada. The effects of temperature on BH treatment, including BH at 42 °C (BH42), 42 °C followed by 55 °C (BH42+55), 55 °C followed by 42 °C (BH55+42), and 55 °C (BH55) were evaluated for anaerobic digestion performance enhancement and compared with TH treatment at 165 °C. The TH, BH42, BH42+55, BH55+42, and BH55 treatments caused the reduction of volatile suspended solids (VSS) by 22.6%, 17.5%, 24.6%, 23.1%, and 25.9%, respectively. The soluble chemical oxygen demand (sCOD) content of the sludge increased by 377.5%, 323.8%, 301.3%, 286.9%, and 221.7% by the TH, BH55, BH42+55, BH55+42, and BH42 treatments, respectively. Volatile fatty acids (VFA) constituted around 40% of the sCOD in the BH-treated sludge and 6% in the TH-treated sludge. The cumulative methane yields (NmLCH4/g COD fed) of sludge treated by BH55+42 and TH were respectively 23% and 20% higher than that of the untreated sludge. For BH pretreatment, sludge treated by BH55+42 produced more methane than those treated by BH42+55, BH55, and BH42. The methane yields of the combined sludge treated by the TH and BH55+42 treatments were in the ranges of 248.9 NmLCH4/g COD to 266.1 NmLCH4/g COD fed, and 255.3 NmLCH4/g COD to 282.2 NmLCH4/g COD fed, respectively.

Enhancement of the sludge disintegration and nutrients release by a treatment with potassium ferrate combined with an ultrasonic process

Sludge disintegration by ultrasound is a promising sludge treatment method. In order to enhance the efficiency of the sludge reduction and hydrolysis, potassium ferrate (K2FeO4) (PF) was used. A novel method was developed to improve the sludge disintegration-sludge pretreatment by using PF in combination with an ultrasonic treatment (PF + ULT). After a short-term PF + ULT treatment, 17.23% of the volatile suspended solids (VSS) were reduced after a 900-min reaction time, which is 61.3% higher than the VSS reduction for the raw sludge. The supernatant soluble chemical oxygen demand (SCOD), total nitrogen (TN), volatile fatty acids (VFAs), soluble protein and polysaccharides increased by 522.5%, 1029.4%, 878.4%, 2996.6% and 801.9%, respectively. The constituent parts of the dissolved organic matter of the sludge products were released efficiently, which demonstrated the positive effect caused by the PF + ULT. The enhanced sludge disintegration process further alleviates environmental risk and offers a more efficient and convenient method for utilizing sludge.

Microbial fuel cell technology as a downstream process of a membrane bioreactor for sludge reduction

Recently, microbial fuel cells (MFCs) have been integrated with membrane bioreactors (MBRs), either in an internal or an external configuration, for wastewater treatment and energy recovery. In an external configuration, MFCs could be applied for an efficient sludge reduction since they can simultaneously address energy issue and environmental concerns associated with sludge treatment.In the present study, a potentiostatic controlled microbial fuel cell (MFC) was fed with activated sludge from a membrane bioreactor (MBR) at different total suspended solid (TSS) concentrations (1–10gTSSL−1) in order to assess the electrochemical response of the system and the impact of the bioelectrochemical treatment on sludge characteristics and membrane fouling parameters. The MFC showed COD removals 30% higher than the control test and a reduction of volatile suspended solids (VSS) up to 43% with concomitant production of energy (maximum current density of 2.0Am−2). The electricity production increased with the increase of TSS content. In both MFC and the control test, an increase of soluble microbial products (SMP) ratio in terms of proteins and carbohydrates (SMPp/SMPc) and an average 50% increase of sludge hydrophobicity were observed. This could limit membrane fouling in the case that the sludge is recirculated to the MBR. The electrochemical characterization indicated that both, acetate and sludge oxidation took place at a similar formal potential of −0.2V vs. SHE indicating that both used the same electron transfer mechanism. Hence, this study shows that a MFC could oxidize, reduce and stabilise MBR sludge producing electricity and affecting membrane fouling parameters.

Disintegration impact on sludge digestion process

ABSTRACTThe anaerobic sludge digestion is a widely used method for sludge stabilization in wastewater treatment plant. This process can be improved by applying the sludge disintegration methods. As the sludge disintegration is not investigated enough, an analysis of how the application of thermal hydrolysis affects the sludge digestion process based on full-scale data was conducted. The results showed that the maximum volatile suspended solids (VSS) destruction reached the value of 65% independently on the application of thermal hydrolysis. The average VSS destruction increased by 14% when thermal hydrolysis was applied. In order to have the maximum VSS reduction and biogas production, it is recommended to keep the maximum defined VSS loading of 5.7 kg VSS/m3/d when the thermal hydrolysis is applied and to keep the VSS loading between 2.1–2.4 kg VSS/m3/d when the disintegration of sludge is not applied. The application of thermal hydrolysis leads to an approximately 2.5 times higher VSS loading maintenance comparing VSS loading without the disintegration; therefore, digesters with 1.8 times smaller volume is required.

Physiological adaptation and metabolic property of earthworms in vermifiltration for liquid-state sludge stabilization using bulk stable isotope and specific fatty acid compound stable isotope values

The presence of earthworms in vermifilter (VF) led to the significant stabilization of sludge by enhancing the reduction in volatile suspended solids by 20.9%. The proliferation of earthworms feeding on the sludge was reflected by the observed increase of earthworm biomass, which indicated that earthworms adapt to VF environment well. Further investigation conducted using bulk stable isotope combined with specific fatty acid compound stable isotope technologies to determine physiological adaptation and metabolic property of VF earthworms. The observed injury of cuticle and the dense of goblet cells demonstrated that the earthworm was suffering from environment stress. However, earthworms could adjust their antioxidant enzyme systems to maintain their normal physiological function. Analyses of the bulk stable isotope and specific fatty acid compound stable isotope showed that the physical metabolism of earthworm hatchlings was more active than that of earthworm adults, which suggested that the increasing proportion of earthworm hatchings might be an effective way to optimize earthworm population structure in the VF system. Consequently, the improved treatment performance of sludge stabilization by vermifiltration was realized.

Microbial enzyme and biomass responses: Deciphering the effects of earthworms and seasonal variation on treating excess sludge

This paper reports on a seasonal pattern comparison of microbial enzymatic activities and biomass responses based on a conventional biofilter (BF, without earthworm) and a vermifilter (VF, with earthworm, Eisenia fetida) for excess sludge treatment. The volatile suspended solids (VSS) reduction, viable cell number and enzyme activities were assayed to probe what made the VF operate stably. The results indicated that the earthworm activities can polish the VSS reduction with 27.17% more than the BF. Though the VF had a lower level in the viable cell number compared with the BF, the earthworm strongly improved the microbial enzymatic activities such as INT-dehydrogenase, protease, β-glucosidase and amylase, which can explain the excellent performance of VSS reduction. The correlation analysis documented that the VSS reduction was positively correlated with microbial enzyme activities. More importantly, the earthworm enabled the VF to avoid the detrimental influence of temperature, which guaranteed a stable performance during seasonal variations.

Effect of extended aeration on the fate of particulate components in sludge stabilization

The study investigated the effect of extended aeration on the fate of particulate components of biological sludge in aerobic stabilization. Biological sludge was generated in a fill and draw reactor fed with domestic sewage and sustained at steady state, at a sludge age of 20days. Particulate fractions of sludge were determined by model evaluation of the corresponding oxygen uptake rate profile. Extended aeration could not produce a mineralized biomass. External aerobic stabilization of the thickened sludge achieved a volatile suspended solids reduction of 68% after 60days. High reduction could be attributed to the relatively higher rate for the hydrolysis of accumulated particulate metabolic products, compared to conventional activated sludge. Model evaluation based on death-regeneration mechanism indicated a gradually decreasing decay rate for solids; the first phase could be associated with the inactivation/death of the viable biomass and the second controlled by the slower breakdown of particulate metabolic products.

Impact of alkaline-hydrolyzed biosolids (Lystek) addition on the anaerobic digestibility of TWAS in lab – And full-scale anaerobic digesters

The effect of different Lystek biosolids doses on the anaerobic digestability of thickened waste activated sludge (TWAS) was evaluated in a lab- and full-scale anaerobic digester. The overall findings of this study emphasize the beneficial impact of Lystek addition to the lab- and full-scale anaerobic digesters in terms of enhanced biogas production and increased volatile suspended solids reduction (VSSR) efficiency. Lystek added at 4% by volume to TWAS increased the methane yield from 0.22 to 0.26L CH4/g VSSadded at an solids retention time (SRT) of 10days, and from 0.27 to 0.29L CH4/g VSSadded at an SRT of 15days. Furthermore, the VSSRs of 37% and 47% were observed for the TWAS, and the TWAS with 4% Lystek, while at an SRT of 15days, the observed VSSR were 49% and 58%, respectively. The lab-scale study showed that the influence of Lystek addition on methane yield and solids destruction efficiencies was more pronounced at the shorter SRT, 20% enhancement (SRT of 10d) vs. 9% enhancement (SRT of 15d) for methane yield, and 27% (SRT of 10d) vs. 22% (SRT of 15d) for VSS destruction efficiency improvement. Furthermore, addition of 4% of Lystek to the feed of the full-scale anaerobic digester at St. Marys wastewater treatment plant (WWTP) resulted in a 50% increase in the average specific methanogenic activity and 23% increase in methane yield of the biochemical methane potential tests after eight months. The results showed that Lystek degradation kinetics were 40% faster than the TWAS, as reflected by first order kinetic coefficients of 0.053d−1 and 0.073d−1 for TWAS and Lystek at an SRT of 10days.

Earthworm eco-physiological characteristics and quantification of earthworm feeding in vermifiltration system for sewage sludge stabilization using stable isotopic natural abundance

Previous studies showed that the presence of earthworm improves treatment performance of vermifilter (VF) for sewage sludge stabilization, but earthworm eco-physiological characteristics and effects in VF were not fully investigated. In this study, earthworm population, enzymatic activity, gut microbial community and stable isotopic abundance were investigated in the VF. Results showed that biomass, average weight, number and alkaline phosphatase activity of the earthworms tended to decrease, while protein content and activities of peroxidase and catalase had an increasing tendency as the VF depth. Earthworm gut microbial communities were dominated by Gammaproteobacteria, and the percentages arrived to 76–92% of the microbial species detected. 15N and 13C natural abundance of the earthworms decreased with operation time, and increased as the VF depth. Quantitative analysis using δ15N showed that earthworm feeding and earthworm–microorganism interaction were responsible for approximately 21% and 79%, respectively, of the enhanced volatile suspended solid reduction due to the presence of earthworm. The finding provides a quantitative insight into how earthworms influence on sewage sludge stabilization in vermifiltration system.

Modeling the fate of particulate components in aerobic sludge stabilization--performance limitations.

The study investigated the effect of sludge composition on the limitations of aerobic stabilization. It was designed with the foresight that the stabilization mechanism could only be elucidated if the observed volatile suspended solids reduction were correlated with the fate of particulate components in sludge. Biomass sustained at sludge ages of 2 and 10 days were used in the stabilization reactors. Particulate components were determined by model evaluation of corresponding oxygen uptake rate profiles. Interpretation of the experimental data by modeling, based on death-regeneration mechanism without external substrate, could simulate the fate and evolution of major components in sludge during stabilization. It showed that both microbial decay and hydrolysis of non viable cellular material proceeded at much slower rates as compared with biological systems sustained with substrate feeding. Modeling also indicated that particulate metabolic products generated by sludge acclimated to high sludge age undergo slow biodegradation under prolonged stabilization.

PENGARUH PENAMBAHAN TRACE METAL FE TERHADAP PENYISIHAN KANDUNGAN PADATAN LIMBAH CAIR KELAPA SAWIT MENGGUNAKAN REAKTOR HYBRID UPFLOW ANAEROBIC SLUDGE BLANKET

Research about influence the addition of trace metal Fe against allowance for the solid content of palm oil mill effluent using Hybrid Upflow Anaerobic Sludge Blanket Reactor aim to know the additionof trace metal Fe against allowance for the solid content of palm oil mill effluent using HUASB reactor based on removal of Chemical Oxygen Demand (COD), Total Suspended Solid (TSS) dan Volatile Suspended Solid (VSS). The reactor isa reactor with a combination of suspended growth reactor in the bottom and attached growth reactor at the top. The material used is palm oil mill effluent and inoculum derived from PKS Pagar Merbau. Test parameters to observed are COD, TSS and VSS. The optimum conditions obtained on the organic load is 17024 mg/l with the addition of Fe is 0.5 mg/l so that obtained COD reduction is 85.891%, TSS reduction is 86.047% and VSS reduction is 36.566%.

Performance evaluation of the electrolysis process for waste sludge stabilization in decentralization practices

This study was undertaken to evaluate the potential use of electrolysis process for waste sludge stabilization in decentralization practices by focusing on the operating parameters such as sludge composition, detention time, and electric voltage. The laboratory batch scale results show that the sludge extracted from a packed bed biofilm reactor can reach the minimum concentration of 659 mg/L volatile suspended solids (VSS) merely within 5 h detention time at an applied voltage of 2 V, whereas the most identical level is obtained from activated sludge by 7 h with 3.6 V. The soluble COD in the supernatant phase of the former process would be increased to 297 mg/L by means of 27% VSS reduction. The economical pre-estimation indicates that electrolysis is more sustainable if stand as a preconditioning stage of biological digestion by 70% capital and operating cost reduction. This configuration can also cause occupying 54% lesser footprint area of aerobic digestion with total average reduction of 56% VSS within 77 h. The biological assay on digested product was also determined with reference to the growth of Phragmites sp. plant. This study recommends the electrolysis-pretreated conditioning waste sludge followed by aerobic digestion incorporating with attached growth biological systems as a valuable process in decentralization.

Rate control-based strategy to enhance biological nitrogen removal during anoxic/oxic sludge digestion

Anoxic/oxic (A/O) sludge digestion is a waste-activated sludge (WAS) treatment practice that simultaneously reduces volatile suspended solids reduction and removes nutrients from digested sludge. This study aims to optimize the performance of A/O sludge digestion by achieving the optimum alkalinity and nitrogen balance through rate control. Rate control involves oxic/anoxic cycling based on the activity of WAS (i.e. ammonification, nitrification, oxygen utilization, and denitrification rates) and controlling the processes of amonification, nitrification, oxygen ultilization, and denitrification in WAS. This strategy is different from pH, oxidation–reduction potential, dissolved oxygen controls, or fixed time control methods. Laboratory-scale batch aerobic digestion and A/O digestion tests were performed to verify the feasibility of the approach. The optimum operational cycles for the aeration and mixing were determined as 3.5 and 2.5 h, respectively (6 h full cycle). The sludge reduction in A/O digestion was greater than that in the aerobic digestion (51.83 vs. 48.13%) at a sludge retention time of 23 d. The total nitrogen reduction in A/O digestion was significantly higher than that in the aerobic digestion (65.20 vs. 12.27%). The performance of the proposed rate-control strategy for A/O digestion is superior to those of other experimental control schemes. In addition, this technique produces a sludge dewatering liquor with low nitrogen and phosphorus concentrations.

Extent of endogenous decay and microbial activity in aerobic stabilization of biological sludge

The study evaluated the role of endogenous decay and microbial activity in aerobic stabilization of biological sludge. Biomass acclimated to acetate in a fill and draw reactor operated at a sludge age of 8 d was subjected to aerobic stabilization with no external substrate for a period of 70 days. Achieved volatile suspended solids reduction remained limited to around 43% after 30 days. The magnitude of endogenous decay, presumably responsible for stabilization, was quite different with bH values of 0.21/d and 0.06/d depending on the implemented respirometric procedure. Model profiles simulated with these values could not predict the observed VSS profile, mainly due to the accumulation of particulate metabolic products and residual organic cellular debris of disintegrated biomass during the process providing conclusive evidence that the total organic content of the stabilized biomass cannot be reduced below a critical level by means of biological processes.