Anaerobic digestion of ultrasonicated sludge at different solids concentrations - Computation of mass-energy balance and greenhouse gas emissions

Anaerobic digestion of thermal pre-treated sludge at different solids concentrations – Computation of mass-energy balance and greenhouse gas emissions

Predicting the apparent viscosity and yield stress of digested and secondary sludge mixtures

Greenhouse gas emissions in sludge ultrasonication followed by anaerobic digestion processes

Fenton pre-treatment of secondary sludge to enhance anaerobic digestion: Energy balance and greenhouse gas emissions

Microwave irradiation is a novel and very promising technology for sludge conditioning. As pretreatment, it has a verified beneficial effect on the microbial degradation and anaerobic digestion of sewage sludge, but in present work we dealt with the applicability of microwave pretreatments for food industrial sludge. However, studies cannot be found that specialize on the effects of the MW treatments with different intensities on the anaerobic digestion of sludge. In our work we focused on the examination of the effect of MW pretreatment for 0.5, 2.5, and 5 W/g on the carbonaceous biochemical oxygen demand (CBOD5), solubilization of organic matters (sCOD/tCOD), and the mesophilic anaerobic digestion of dairy sewage sludge. It can be concluded that the MW pretreatments were appropriate to enhance the efficiency of anaerobic digestion. With MW pretreatments the specific biogas product could be increased from 220 mL g−1 to more than 600 mL g−1 because of the increased solubility (from 9.7% to more than 40%), and the enhanced accessibility of organic compounds for decomposing bacteria. © 2010 American Institute of Chemical Engineers Environ Prog, 2011

A short bibliographic review concerning biomethane production from wastewater sludge.

Anaerobic digestion of sludge is considered to be one of the most appropriate technologies for energy production via conversion of organic matter into methane containing biogas. Biogas produced by anaerobic digestion of municipal wastewater sludge can be utilized as fuel to offset heat and electricity consumption of wastewater treatment facilities. Modeling can be used effectively to evaluate the impact of different process and operation variables on the performance of the treatment processes including complex ones such as anaerobic digestion. Therefore, the Anaerobic Digestion Model No. 1 (ADM1) was applied in order to evaluate the performance of a full-scale anaerobic sludge digester in this study. With the calibration of the most sensitive parameters used in the ADM1, model outputs corresponded well with the measured data obtained from the operation of the full-scale digester. The model was validated with the data acquired from the same anaerobic digester at a different operation period (360days) and simulation results successfully predicted the digester performance. The overall results of this study demonstrated that the ADM1 can be used as a very useful tool to simulate the digestion of mixed sludge generated from full-scale wastewater treatment plants under mesophilic conditions.

Life cycle assessment of sludge anaerobic digestion combined with land application treatment route: Greenhouse gas emission and reduction potential

Mesophilic and thermophilic anaerobic digestion of primary and secondary sludge. Effect of pre-treatment at elevated temperature

New insight into volatile sulfur compounds conversion in anaerobic digestion of excess sludge: Influence of free ammonia nitrogen and thermal hydrolysis pretreatment

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.

This study analyzed greenhouse gas (GHG) emissions from a wastewater treatment plant (WWTP) that uses a combination of physical, chemical, and biological processes and estimated the emissions generated from treatment of oil-rich wastewater from a locomotive repair factory in China. The WWTP produces 526.8 t CO2-equivalent/a corresponding to 4.3 t CO2-equivalent/t oil removed. The combustion of fossil fuels for onsite energy generation is the major source of GHG, accounting for 79.7% of overall emissions. Use of chemicals for metal cleaning, flocculation, and pH control accounts for 13.4% emissions; anaerobic digestion accounts for 3.8% emissions; and the transport of solid waste and subsequent generation of landfill biogas account for 3.1% emissions. Theoretical analysis of various process design alternatives demonstrated that the recovery of biogas produced during anaerobic sludge digestion and its use as fuel reduces the emissions of GHG by 93.9 t CO2-equivalent/a, which is 15.1% of the overall emissions of the treatment plant. The use of aerobic digestion instead of anaerobic digestion in this plant did not significantly effect GHG emissions. Using anaerobic digestion for sludge treatment and releasing the generated CH4 into the atmosphere without further flaring or recovery increased GHG emissions the greatest. The reuse of waste oil and proper management of solid waste are recommended as effective ways of reducing GHG emissions.

Processing of the produced primary and secondary sludge during sewage treatment is demanding and requires considerable resources. Most common practices suggest the cotreatment of primary and secondary sludge starting with thickening and anaerobic digestion. The aim of this study is to investigate the anaerobic digestion of the primary sludge only and estimate its impact on sludge treatment and energy recovery. Within this context, the performance of the anaerobic digestion of primary sludge is explored and focused on practices to further enhance the methane production by using additives, e.g., a cationic polyelectrolyte and attapulgite. The results showed that the overall yield in methane production during anaerobic digestion of primary sludge alone was higher than that obtained by the anaerobic digestion of mixed primary and secondary sludge (up to 40%), while the addition of both organic polyelectrolyte and attapulgite enhanced further the production of methane (up to 170%). Attapulgite increased the hydrolysis rate of biosolids and produced relatively stabilized digestate, though of lower dewaterability. Moreover, the results suggest that single digestion of primary sludge may accomplish higher methane production capacities at lower digestors’ volume increasing their overall efficiency and productivity, while the produced digestates are of adequate quality for further utilization mainly in agricultural or energy sectors.

Effect of mixed primary and secondary sludge for two-stage anaerobic digestion (AD)

BACKGROUND: Process modeling is a useful tool for description and prediction of the performance of anaerobic digestion systems under varying operation conditions. The objective of this study was to implement a model to simulate the dynamic behavior of a large-scale anaerobic sewage sludge digestion system. Artificial neural network (ANN) models using algorithms best suited to environmental problems (the Levenberg–Marquardt algorithm and the ‘gradient descent with adaptive learning rate’ back propagation algorithms) were used to model the anaerobic sludge digester of the Ankara Central Wastewater Treatment Plant (ACWTP) using dynamic data. RESULTS: Based on the relatively low mean square error (MSE), mean absolute error (MAE) and mean absolute percentage error (MAPE) and very high r values, ANN models predicted effluent volatile solid (VS) concentration and methane yield satisfactorily. Effluent VS and methane yields were predicted by the ANN using only conventional parameters such as pH, temperature, flow rate, volatile fatty acids, alkalinity, dry matter and organic matter. The best back propagation algorithm was the gradient descent with adaptive learning rate algorithm in both models. In the training of the neural network, four-fold cross-validation was used for validation of the model for better reliability. CONCLUSION: The proposed ANN models were shown to be capable of dynamically predicting the VS and CH4 production rates for real system behavior. Only relatively simple monitoring parameters are needed to build the model for this complex anaerobic digestion process. Copyright © 2011 Society of Chemical Industry