Sewage Sludge Processing Research Articles

Investigation on the mercury nucleation mechanism based on the release characteristics of inhalable particles during coupled combustion of sewage sludge-coal washery tailing

Establishing an integrated treatment technology system for sewage sludge and coal washery tailing by mixed combustion can effectively overcome the disadvantages of the low calorific value and utilization efficiency, realizing the efficient resource. The single-component and coupled fuel were analyzed. Aiming at the generated inhalable particulate matter during the combustion process, using multiple characterization means and the fluidized bed experimental system, the micro-characteristics and elemental distribution of coupled fuel and combustion products were obtained, and the theory based on nucleation control was analyzed to reveal particle size distribution and particulate matter emission characteristics under multiparameter coupling conditions. The nucleation mechanism of Hg on the surface of the particulate matter under mixed combustion conditions was clarified. The results show that the weight loss process of sewage sludge in the combustion process mainly includes four stages. An obvious boundary between the volatilization and combustion processes of fixed carbon does not exist; furthermore, there is some overlap between the two processes. Volatiles and minerals interact in the mixed combustion process. The constituent elements of PM1 and PM1∼10 in the generated particulate matter are mainly easily vaporizable and refractory elements, respectively. The particle size of the particles produced presents the characteristics of bimodal distribution. There is a critical value (800 °C) for the influence of combustion temperature on the emission characteristics of particulate matter. It mainly affects the emission characteristics of coarse and fine particles through dominating the occurrence forms of tar, easily gasified and refractory elements, and the collision and aggregation process between particles. Homogeneous nucleation and heterogeneous condensation are the basic pathways for the transition of Hg from the gas phase to particle nucleation, and there are different nucleation control mechanisms. The heterogeneous condensation process includes diffusion control and surface reaction control. In addition, after the coupled fuel is demineralized by acid washing, the nucleation control mechanism changes significantly from diffusion control to chemical reaction control for the particles in the continuum region.

Effects of Magnetic Biochar Addition on Mesophilic Anaerobic Digestion of Sewage Sludge.

As a low-cost additive to anaerobic digestion (AD), magnetic biochar (MBC) can act as an electron conductor to promote electron transfer to enhance biogas production performance in the AD process of sewage sludge and has thus attracted much attention in research and industrial applications. In the present work, Camellia oleifera shell (COS) was used to produce MBC as an additive for mesophilic AD of sewage sludge, in order to explore the effect of MBC on the mesophilic AD process and its enhancement mechanism. Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrometry (FTIR), and X-ray diffraction (XRD) further confirmed that biochar was successfully magnetized. The yield of biogas from sewage sludge was enhanced by 14.68-39.24% with the addition of MBC, and the removal efficiency of total solid (TS), volatile solids (VS), and soluble chemical oxygen demand (sCOD) were 28.99-46.13%, 32.22-48.62%, and 84.18-86.71%, respectively. According to the Modified Gompertz Model and Cone Model, the optimum dosage of MBC was 20 mg/g TS. The maximum methane production rate (Rm) was 15.58% higher than that of the control reactor, while the lag-phase (λ) was 43.78% shorter than the control group. The concentration of soluble Fe2+ and Fe3+ were also detected in this study to analyze the function of MBC for improving biogas production performance from sewage sludge. The biogas production was increased when soluble Fe3+ was reduced to soluble Fe2+. Overall, the MBC was beneficial to the resource utilization of COS and showed a good prospect for improving mesophilic AD performance.

Technological, Ecological, and Energy-Economic Aspects of Using Solidified Carbon Dioxide for Aerobic Granular Sludge Pre-Treatment Prior to Anaerobic Digestion.

The technology of aerobic granular sludge (AGS) seems prospective in wastewater bio-treatment. The characteristics as well as compactness and structure of AGS have been proved to significantly affect the effectiveness of thus far deployed methods for sewage sludge processing, including anaerobic digestion (AD). Therefore, it is deemed necessary to extend knowledge on the possibilities of efficient AGS management and to seek viable technological solutions for methane fermentation of sludge of this type, including by means of using the pre-treatment step. Little is known about the pre-treatment method with solidified carbon dioxide (SCO2), which can be recovered in processes of biogas upgrading and enrichment, leading to biomethane production. This study aimed to determine the impact of AGS pre-treatment with SCO2 on the efficiency of its AD. An energy balance and a simplified economic analysis of the process were also carried out. It was found that an increasing dose of SCO2 applied in the pre-treatment increased the concentrations of COD, N-NH4+, and P-PO43- in the supernatant in the range of the SCO2/AGS volume ratios from 0.0 to 0.3. No statistically significant differences were noted above the latter value. The highest unit yields of biogas and methane production, reaching 476 ± 20 cm3/gVS and 341 ± 13 cm3/gVS, respectively, were obtained in the variant with the SCO2/AGS ratio of 0.3. This experimental variant also produced the highest positive net energy gain, reaching 1047.85 ± 20 kWh/ton total solids (TS). The use of the higher than 0.3 SCO2 doses was proved to significantly reduce the pH of AGS (below 6.5), thereby directly diminishing the percentage of methanogenic bacteria in the anaerobic bacterial community, which in turn contributed to a reduced CH4 fraction in the biogas.

Prediction of hydrogen yield from supercritical gasification process of sewage sludge using machine learning and particle swarm hybrid strategy

This study presents an integrated framework of machine learning models (Artificial Neural Network, Ensembled Learning Tree, Support Vector Machine, and Gaussian Process Regression) and particle swarm optimization (PSO) to predict and optimize hydrogen production from SCWG using sewage sludge characteristics and process parameters. According to the results, ELT-PSO is preferred for forecasting hydrogen yield (Coefficient of determination (R2) = 0.997, Root Mean Square Error (RMSE) = 0.093), and it is highly suggested for handling complex variable-target correlation. However, Support Vector Machine (SVM) performed poorly, with R2 = 0.83 and RMSE = 2.28. According to SHAP feature importance Temperature, Carbon, Hydrogen, and Pressure are among the parameters that have strong impact. In addition, by adjusting the ML hyperparameters, optimization method (PSO) was used to maximize H2 yield. The optimized ELT-PSO model was utilized to establish a Graphical User Interface that made it simple to calculate H2 yield.

Assessing Different Inoculum Treatments for Improved Production of Hydrogen through Dark Fermentation

Hydrogen gas (H2) is an energy carrier that does not generate carbon dioxide emissions during combustion, but several processes in use for its production demand high energy inputs associated with fossil fuels and greenhouse emissions. Biological processes, such as dark fermentation (DF), have the potential to remove the dependency on fossil fuels in H2 production. DF is a process that encourages fermentative bacteria to ferment organic substrates to produce H2 as a truly clean energy carrier, but its success depends on removing the presence of competing H2−consuming microorganisms in the inoculum consortia. This paper addresses a strategy to enhance H2 production from different types of substrates by testing inoculum pre-treatment processes to inactivate H2−consuming bacteria, including acid-shock (pH 3), basic-shock (pH 10) and heat-shock (115 °C) methods. Digestate from anaerobic digesters processing sewage sludge was used to produce pre-treated inocula, which were subsequently tested in a batch bio-H2 potential (BHP) test using glucose as a substrate. The results show that heat-shock pre-treatment was the best method, reporting a H2 yield of 191.8 mL-H2/gVS added (the untreated inoculum reported 170.91 mL-H2/gVS added). Glucose conversion data show a high concentration of butyric acid in both treated and untreated inocula during BHP tests, which indicate that the butyrate pathway for H2 production was dominant; shifting this to the formate route could further enhance net H2 production. A standardised inoculum-conditioning method can help to consistently assess the biohydrogen potential of suitable feedstock for DF and maximise H2 yields.

Russian experience in the use of chemical water treatment waste in economic activity: prospects for use in the treatment of sewage sludge (review article)

PURPOSE. To consider the experience of using chemical water treatment waste in economic activity. To analyze scientific publications of Russian and foreign authors in order to determine the most popular industries in this waste and information about projects already implemented in Russia and abroad. To provide a brief analysis of the main areas of processing and disposal of sewage sludge in the world and in Russia. To assess the prospects for the use of chemical water treatment waste in the treatment of sewage sludge.METHODS. To achieve this goal, an assessment of the environmental impact of chemical water treatment waste on the environmental situation and human health was carried out on the example of Kazan CHP-1 (KTEC-1). A number of studies of KTEC-1 carbonate sludge have been carried out to determine the granulometric and elemental composition. results. The physico-chemical composition of carbonate sludge depends on a number of parameters of the water treatment system at an energy facility: the process of liming and coagulation of water, the amount of insoluble salts, the dewatering technology used, etc. Carbonate sludge is insoluble in water, has a typical chemical composition containing calcium carbonate (CaCO3), calcium oxide (CaO), magnesium carbonate (MgCO3), magnesium oxide (MgO), iron hydroxide (Fe(OH)3), silicon dioxide (SiO2), etc.CONCLUSION. The use of this type of technological process makes it possible to reduce the amount of calcium oxide used and replace it with calcium oxide from carbonate sludge. The use of carbonate sludge as a sediment stabilizer due to the CaO content is confirmed by laboratory studies. Due to these data, the disposal of chemical water treatment waste is ensured, less pollution of environmental objects is achieved.

Sewage Sludge Biorefinery for Circular Economy

Sewage sludge processing and disposal have a significant weight on the energy and economic balances of wastewater treatment operations and contribute substantially to greenhouse gas emissions related to wastewater processing. Despite this, sewage sludge contains substantial recoverable resources in the form of energy and useful molecules. The current challenge, other than reducing the environmental and economic impacts of its disposal, is to recover energy and materials from this waste stream, implementing a biosolid-centered circular economy with the greatest possible added value. A number of options along these lines exist, and others are being investigated, ranging from biological processes, thermochemical technologies, bioelectrochemical processing, biorefineries and others. Recoverable resources comprise biogas from sludge fermentation, liquid and solid end products (e.g., biodiesel and biochar) and valuable nutrients (N and P). This paper presents a state of the art of biorefinery, with emphasis on recent developments in non-conventional resource recovery from EBSS streams for sludge-based circular economy implementation. Expectations and limitations, including technological readiness, of these technologies are discussed.

Multi-functional of TiO2@Ag core–shell nanostructure to prevent hydrogen sulfide formation during anaerobic digestion of sewage sludge with boosting of bio-CH4 production

Herein, we report a novel supplement called TiO2@Ag core–shell nanostructure that revealed a high removal of hydrogen sulfide gas with boosting the bio-methane production from the anaerobic digestion process of sewage sludge. TiO2@Ag core–shell nanostructure was synthesized by the deposition of Ag shell NPs on TiO2 core NPs using a reduction method. The prepared samples of the core–shell and its components were characterized using different techniques such as XRD, SEM, TEM and AFM. A concentration of TiO2@Ag core–shell NS (50 mg/L) was supplemented with anaerobic bioreactors to study their effect on the removal of hydrogen sulfide from the anaerobic digestion of sewage sludge compared to silver and titanium dioxide nanoparticles alone. The results showed a 3-fold increase in the produced bio-methane upon the use of TiO2@Ag core–shell NS with a high removal of hydrogen sulfide (91.9 %) compared to using only silver nanoparticles or titanium dioxide nanoparticles. Concisely, the prepared TiO2@Ag core–shell NS was multifunctional and more active than its components in removing hydrogen sulfide, enhancing bio-methane production, and detoxifying hazardous materials from sewage sludge.

Insight into the Effects of Inorganic Element Catalysis and Basic Fuel Properties on the Self-Sustained Smoldering Process of Sewage Sludge

The objective of this study is to investigate the effects of inorganic element catalysis and basic fuel properties of sewage sludge on pyrolysis kinetics and self-sustained smoldering characteristics. The sludge pyrolysis process was explored by thermogravimetric and iso-conversion methods, and it was found that the pyrolysis process can be divided into two stages, which are mainly determined by the organic and inorganic components of the fuel. The inorganic components (e.g., Na, Fe and Mn) have a significant catalytic effect on the release of volatiles and the decomposition of macromolecules. The smoldering experiment revealed that the smoldering front and the evaporation front propagated at stable but different speeds. Among the five fuels, SS4 has the highest smoldering temperature (1070 °C) and the lowest propagation velocity (0.7 cm/min of smoldering velocity and 0.3 cm/min of evaporation velocity), while the carbon density mainly determines the heat release in the oxidation process, and the inorganic elements play a significant catalytic role at different temperatures. The obtained thermodynamic and smoldering characteristics facilitate the development and optimization of the disposal of sewage sludge, emphasizing the importance of considering feedstock composition.

Sewage sludge dewatering by electric field

During the cleaning and further treatment of municipal wastewater, sediments are formed, which are extremely dangerous from a sanitary and hygienic point of view, poorly dewatered, have high humidity (over 90%), large volumes (up to 3% of wastewater consumption), contain organic substances, pathogens, heavy metals, etc. In Ukraine, at most wastewater treatment plants, sewage sludge is mostly piled up on sludge sites after minimal treatment. Effective processing and disposal of sewage sludge in order to reduce the negative impact on the environment, as well as the use of sewage sludge as secondary raw materials, is an actual, complex and urgent task. The key link in the existing process of treatment and disposal of sewage sludge is their dewatering. When designing facilities for the treatment and disposal of sewage sludge, advanced technologies should be used, the use of which is based on scientific and technical research. The article reviews the results of research on the intensification of existing mechanical methods of sewage sludge. One of the most effective methods of intensifying the process of dewatering sewage sludge is electro-dewatering, which involves the application of an electric field during mechanical dewatering of sludge. Electro-dewatering technology makes it possible to reduce the humidity of sediments to 20...40%, reduce the concentration of heavy metals and pathogens in sediments, etc. The purpose of this work is to study the possibility of electro-dewatering of activated sludge from secondary settling tanks of municipal wastewater treatment plants in Lviv. Empirical research methods were used. A laboratory scale has been designed for electro-dewatering of sewage sludge. Activated sludge with a moisture content of 98% was studied. It is shown that the effect of activated sludge dewatering, depending on the duration of its treatment, is an S-shaped curve that resembles a kinetic autocatalytic reaction with three periods: induction, main, and fading. The possibility of electro-dewatering of sewage sludge with a maximum dewatering effect of 60% has been proven. Therefore, it is proposed to carry out mechanical dewatering of city sewage sludge using an electric field.

Chemicals and Fuels from Biomass via Fischer–Tropsch Synthesis: A Route to Sustainability

This unique study combined the lab and full scales to investigate how the anaerobic digestion process of sewage sludge was affected by a temperature change within the lower mesophilic temperature range (32–37.5 °C). Both scientific methane potential experiments and dewaterability studies were made to be used in changes of the operational conditions for a full-scale wastewater treatment plant. The aim of this study was to reduce anaerobic digestions heat consumption by altering the operational mesophilic temperature in first lab-scale experiments and then in continuation to full-scale conditions. The results of the study suggest that it is possible to save approximately 13% in heat energy demand each year by reducing the temperature for anaerobic digestion by 2.5 °C. At the lab scale, the effect of temperature on biogas production was tested in a batch experiment by measuring the biochemical methane production. At 32 °C, the production of biogas decreased by 11% compared to that at 37.5 °C. No significant difference was observed between 37.5 °C and 34.5 °C. The effect of temperature on sludge dewaterability was tested by measuring the capillary suction time, and no difference was detected between various temperatures. To confirm these results, the temperature in two full-scale digesters was gradually adjusted from 37.5 °C to 35 °C. No change was observed in biogas production, process stability, or dewaterability. The amount of heat energy that can be saved for the full-scale digesters was calculated using a heat balance. This study shows that it is possible to reduce the heat demand for AD in real applications without compromising the biogas production and process stability.

The dewatering performance and cracking-flocculation-skeleton mechanism of bioleaching-coal fly ash combined process for sewage sludge

High water content in sludge will affect the transportation and subsequent disposal of sludge. Bioleaching is a biological sludge conditioning technology, which can effectively improve the dewatering performance of sludge and reduce the content of heavy metals in sludge. Coal fly ash, as a skeleton builder, can also improve the dewatering performance of sludge. In this study, bioleaching combined with coal fly ash (BL-CFA) process was employed to improve sludge dewatering performance. Based on the results of response surface methodology (RSM), the capillary suction time (CST) and water content (WC) of sludge decreased by 52.27% and 38.92%, respectively. The dewatering effect of BL-CFA is superior compared with single process. For extracellular polymeric substances (EPS), the content of protein and polysaccharide in tightly and loosely EPS (TB-EPS and LB-EPS) of sludge decreased after BL-CFA process, while that in soluble EPS (S-EPS) increased. Three-dimensional fluorescence indicated that the weakened fluorescent areas of proteinoid and soluble microbial by-product-like (SMP) organic in LB-EPS and TB-EPS, which is beneficial to the improvement of sludge dewatering performance. Fourier transform infrared (FTIR) spectroscopy showed that the polysaccharides and proteins in the sludge were cleaved and released into the supernatant after BL-CFA process. The variation of particle size revealed that flocculation occurred after adding CFA into acidified sludge, and a supporting structure was formed in the sludge with the assist of CFA through the analysis of the scanning electron microscopy (SEM). Based on the above results, a triple dehydration mechanism was proposed for BL-CFA process, namely, cracking-flocculation-skeleton construction, which endows the combined process with superior sludge dewatering effect and application potential.

The impact of sewage sludge processing on the safety of its use

Particular attention is devoted to pharmaceutical residues in sewage sludge caused by their potential ecotoxicological effects. Diclofenac, ibuprofen and carbamazepine, 17-α-ethinylestradiol, β-estradiol, were analysed in four types of fertilizers, based on sewage sludge commercial products, in compliance with Polish requirements. The release of active pharmaceutical compounds from fertilizers to water the phase after 24 h and 27 days was analysed. Solid-water partition coefficients (Kd) and partitioning coefficient values normalized on organic carbon content (log KOC) were evaluated. The environmental risk to terrestrial ecosystems, due to the application of fertilizers onto soils, was estimated. Cumulative mass of pharmaceuticals emitted to water from fertilizers ranged from 0.4 to 30.8 µg/kg after 24 h contact. The greatest amount of the material that was released, over 70%, was observed for carbamazepine. No presence of compounds except ibuprofen was observed after 27 days of testing. The highest environmental risk in fertilizers is due to carbamazepine, risk quotation, RQ = 0.93 and diclofenac RQ = 0.17. The values of risk quotation estimated for soil were below RQ = 0.01. This fact means that no risk to terrestrial ecosystems is expected to occur. The important decrease of the concentrations of active compounds after passing from sewage sludge to fertilizers [and] to fertilized soil could be observed.

Effects of adding biochar on the preservation of nitrogen and passivation of heavy metal during hyperthermophilic composting of sewage sludge

ABSTRACT Hyperthermophilic composting (HTC) is regarded as an effective method for processing sewage sludge. The aim of the study was to investigate effects of using biochar as an amendment on the preservation of nitrogen and passivation of heavy metal during the HTC process of sewage sludge. Results showed that HTC improved the fermentation efficiency and the compost maturity by increases in the temperature and germination index (GI) value, and decreases in the moisture and C/N ratio compared to conventional thermophilic composting. HTC process and the biochar addition resulted in a decrease of the nitrogen loss compared with the control pile during composting by promoting transforming ammonium into nitrite nitrogen. Adding biochar to composting inhibited the transformation of Cu, Zn and Pb into more mobile speciation compared to the control pile although their contents increased during composting, which lead to reduction in availability of heavy metals. Thus, HTC process with the addition of biochar is viable for the reduction of the nitrogen losses and mobility of heavy metal in compost. Implications: The treatment of sewage sludge is imminent due to its threat to general health and ecosystems. This work represents the effects of adding biochar on the preservation of nitrogen and passivation of heavy metal during hyperthermophilic composting of sewage sludge. Our results indicate that the additions of biochar and hyperthermophilic composting engendered the several of positive effects on the preservation of nitrogen and passivation of heavy metal. Thus, HTC process with the addition of biochar is viable for the reduction of the nitrogen losses and mobility of heavy metal in compost.

Influence of dissolved organic matter on methylmercury transformation during aerobic composting of municipal sewage sludge under different C/N ratios

Current knowledge about the transformation of total mercury and methylmercury (MeHg) in aerobic composting process is limited. In this study, the composition and transformation of mercury and dissovled organic matter (DOM) in aerobic composting process of municipal sewage sludge were were comprehensively characterized, and the differences among the three C/N ratio (20, 26 and 30) were investigated. The main form of mercury in C/N 20 and 26 was organo-chelated Hg (F3, 46%-60%); while the main form of mercury in C/N 30 was mercuric sulfide (F5, 64%-70%). The main component of DOM in C/N 20 and 26 were tyrosine-like substance (C1, 53%-76%) while the main fractions in C/N 30 were tyrosine-like substance (C1, 28%-37%) and fulvic-like substance (C2, 17%-39%). The mercury and DOM varied significantly during the 9 days composting process. Compared to C/N 20 and 26, C/N 30 produced the less MeHg after aerobic composting process, with values of 658% (C/N 20), 1400% (C/N 26) and 139% (C/N 30) of the initial, respectively. Meanwhile, C/N 30 produced the best compost showed greater degree of DOM molecular condensation and humification. Hg fraction had been altered by DOM, as indicated by a significant correlation between mercury species and DOM components. Notably, C/N 30 should be used as an appropriate C/N ratio to control the methylation processes of mercury and degration of DOM.

Propagation of antibiotic resistance genes during anaerobic digestion of thermally hydrolyzed sludge and their correlation with extracellular polymeric substances

The positive impact of the thermal hydrolysis process (THP) of sewage sludge on antibiotic resistance genes (ARGs) removal during anaerobic digestion (AD) has been reported in the literature. However, little information is available on how changes in different extracellular polymeric substances (EPS) due to THP can influence ARG propagation during AD. This study focused on systematically correlating EPS components and ARG abundance in AD of sewage sludge pretreated with THP (80 °C, 110 °C, 140 °C, 170 °C). THP under different conditions improved sludge solubilization followed by improved methane yields in the biochemical methane potential (BMP) test. The highest methane yield of 275 ± 11.5 ml CH4/g COD was observed for THP-140 °C, which was 40.5 ± 2.5% higher than the control. Increasing THP operating temperatures showed a non-linear response of ARG propagation in AD due to the rebound effect. The highest ARGs removal in AD was achieved with THP at 140 °C. The multivariate analysis showed that EPS polysaccharides positively correlated with most ARGs and integrons, except for macrolides resistance genes. In contrast, EPS protein was only strongly correlated with β-lactam resistance genes. These results suggest that manipulating THP operating conditions targeting specific EPS components will be critical to effectively mitigating the dissemination of particular ARG types in AD.

Distribution, Dissemination and Fate of Antibiotic Resistance Genes During Sewage Sludge Processing—a Review

Distribution, Dissemination and Fate of Antibiotic Resistance Genes During Sewage Sludge Processing—a Review

Influence of waste type with co-digestion system on methane production of patch digester stirred with exhaust gases

Investing in biogas is a viable option for the production of renewable energy. Production of renewable energy such as biogas has an impact on improving the environmental function and health impacts for all beneficiaries such as humans, lands, and ecosystems. As well recycling of solid waste could be considered waste management for economic development and protection of degraded and polluted lands. Anaerobic co-digestion has been practically applied in sewage sludge processing, agricultural and waste treatment and is recognized as an economical effective way for waste reuse, treatment, and disposal. This paper presents three co-digestion experimental batches for thickened sludge with food waste, rice straw and cow waste. The mixtures were digested for thirty days, with 15 minutes of daily stirring using laboratory generator exhaust. A steel fixed dome anaerobic digester was used for experimental batches. The produced methane was recorded to be 65 %, 45.9 %, and 55 % when using thickened sludge with food waste, rice straw and cow waste, respectively. Cumulative methane was investigated for 7, 15 and 30 days to show the effect of time in methane production. The results showed that approximately 80 % of the produced methane was produced between 15 and 21 days. Anaerobic co-digestion increases the pH value of the three mixtures. The pH value was increased during anaerobic co-digestion due to the mineralization of the organic matter. However, pH values stayed between 6.0 and 8.0, which is better for growing and activating the methanogenic microorganisms as a reason for methane formation.

Assessing the syngas biomethanation in anaerobic sludge digestion under different syngas loading rates and homogenisation

Gasification offers digestate conversion into syngas, which can be metabolised to CH4 by a mixed anaerobic consortium. However, low gas-liquid mass transfer and CO presence can limit further scale-up. The present study assessed syngas biomethanation (55% H2, 45% CO) in a thermophilic lab-scale continuous anaerobic digester processing sewage sludge. Different syngas loading rates and mechanical stirring compared to pneumatic mixing were investigated. Results showed that anaerobic culture acclimation for CO utilisation is unnecessary. Moreover, the mechanical stirring replacement for the pneumatic system enhanced the gas-liquid mass transfer rate. Hence, the biological conversion of CO and H2 was improved by 30%. Nevertheless, increased pH to 8.6 resulted in acetic acid accumulation (>7.5 g/L). These findings improve syngas biomethanation efficiency and suggest including a proper pH control before further scale-up.

Wastewater Treatment and Biogas Production: Innovative Technologies, Research and Development Directions

The development of wastewater treatment methods and the processing of sewage sludge is associated with the search for new, efficient and technologically justified solutions, the use of which will be an alternative to the systems used thus far [...]