Anaerobic digestate as a nutrient medium for the growth of the green microalga Neochloris oleoabundans

Attempts to alleviate inhibitory factors of anaerobic digestate for enhanced microalgae cultivation and nutrients removal: A review

Combined electrical-alkali pretreatment to increase the anaerobic hydrolysis rate of waste activated sludge during anaerobic digestion

To see the effect of rate of filtration on the removal of suspended solids, the performance of slow sand filters has been studied at laboratory scale using raw water obtained from the nearby canal. The study was conducted using a set of four slow sand filter units operated in parallel. The influent water turbidity applied to the filters was changed by presedimentation. The performance of the filters was measured in terms of the removal of the suspended solids. The filters were found to be quite effective for the removal of the suspended solids after ripening at different filtration rates and raw water quality used in this study.

Microalgae are being increasingly considered as a potential biomass feedstock for various biofuels, biodiesel in particular. Microalgal biomass for biofuel production purposes can be derived by cultivation using several waste resources, such as wastewater or flue gases, due mainly to the absence of the stringent regulations usually applied for food grade health supplements from microalgae. Anaerobic digestion and dark fermentation, the two highly used biomass digestion processes, generate biogas (a mixture of CH4, CO2 and other gases) and a COD (chemical oxygen demand)-rich effluent with leftover organic acids from the fermentation process. Microalgae can utilize the CO2 present in the biogas stream, thus increasing the methane content and improving the fuel properties of biogas. Several reports indicate that certain microalgae are highly tolerant to the high concentrations of methane present in the biogas stream and can effectively utilize the CO2 in photoautotrophic/mixotrophic mode of cultivation to obtain microalgal biomass. The organic acids of the effluent can also be used as a carbon source for mixotrophic/heterotrophic mode of microalgal cultivation, thus providing a cleanup of both the liquid and gaseous effluents of the fermentation process. This chapter describes in detail the capability of microalgae for carbon capture from biogas and their efficiency in the utilization of organic acids from various effluent streams. A biorefinery concept, integrating anaerobic digestion and microalgal cultivation is proposed, and the future perspectives are discussed.

Cultivation of microalgae in the fresh water is not economically feasible, because it requires essential nutrient and light energy for effective biomass yield. Microalgae biomass is capable of valorizing organic and inorganic matter in the wastewater for biofuel yield. Microalgae biomass use freely available solar radiation as light energy and organic and inorganic matter from wastewater as a nutrient source. Direct discharge of urinal wastewater into the environment leads to groundwater contamination. Urinal wastewater mainly composed of essential nutrients such as nitrogen, phosphorus, and potassium. Hence microalgae biomass cultivation is the best option to reduce the inorganic constituent load, and it even biodegrades certain heavy metals. Recovering the freely available nutrients in urinal wastewater by microalgae results in the valuable end product. In addition, the biofuel production from microalgae biomass through anaerobic digestion was a promising technology. The rigid cell wall of microalgae biomass needs to be disintegrated for improving its biodegradability, and the microalgae cultivation with urinal wastewater will be economically viable. This chapter provides the knowledge about nutrient removal from urinal wastewater using microalgae and various types of hydrolysis used for biofuel generation.

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

In this study, the microalga Scenedesmus dimorphus was cultivated phototrophically using unsterilized anaerobic digestate as a nutrient medium. A bench-scale experiment was conducted by inoculating the microalga S. dimorphus with 0.05-10% dilutions of the anaerobic digestate supernatant. It was found that 1.25-2.5% dilutions, which is equivalent to 50-100mgN/L total nitrogen concentrations and 6-12mg P/L total phosphorus concentrations, provided sufficient nutrients to maximize the growth rate along with achieving high concentrations of algal biomass. The microalgae cultivation was scaled up to 100L open raceway ponds, where the effect of paddlewheel mixing on the growth was investigated. It was concluded that 0.3m/s water surface velocity yielded the highest specific growth rate and biomass concentration compared to 0.1 and 0.2m/s. The microalga S. dimorphus was then cultivated in the raceway ponds using 2.5% diluted anaerobic digestate at 317 and 454μmol/(m2×s) average incident light intensities and 1.25% diluted anaerobic digestate at 234 and 384μmol/(m2×s) average incident light intensities. The maximum biomass concentration was 446mg/L which was achieved in the 2.5% dilution and 454μmol/(m2×s) light intensity culture. Moreover, nitrogen, phosphorus, and COD removal efficiencies from the nutrient media were 65-72, 63-100, and 78-82%, respectively, whereas ammonia was completely removed from all cultures. For a successful and effective cultivation in open raceway ponds, light intensity has to be increased considerably to overcome the attenuation caused by the algal biomass as well as the suspended solids from the digestate supernatant.

Anaerobic digestion (AD) appears to be a popular unit operation in wastewater treatment plant to treat waste activated sludge (WAS) and the produced methane gas can be harvested as renewable energy. However, WAS could inhibit hydrolysis stage during AD and hence pre-treatment is required to overcome the issue. This paper aimed to study the effect of electrochemical pre-treatment (EP) towards efficiency of AD using titanium coated with ruthenium oxide (Ti/RuO2) electrodes. The investigation has been carried out using in-house laboratory batch-scale mesophilic anaerobic digester, mixed under manipulation of important operating parameters. Optimization was performed on EP using response surface methodology and central composite design to maximize sludge disintegration and dewaterability. By operating at optimal conditions (pH 11.65, total solids 22,000 mg/L, electrolysis time 35 min, current density 6 mA/cm2, and 1000 mg/L of sodium chloride), the pre-treated WAS in terms of mixed liquor volatile suspended solids (MLVSS) removal, soluble chemical oxygen demand (sCOD), capillary suction time (CST) reduction, and extracellular polymeric substance (EPS) were 38%, 4800 mg/L (increased from 935 mg/L), 33%, and 218 mg/L, respectively. Following AD, the volatile solids (VS) removal and chemical oxygen demand (COD) removal by EP were enhanced from 40.7% and 54.7% to 47.2% and 61.5%, respectively, at steady-state. The biogas produced from control and electrochemical pre-treated WAS were in the ranges of 0.12 to 0.17 and 0.2 to 0.24 m3/kg VSfed, respectively, and the volume of biogas produced was 44–67% over the control. Based on the results obtained, suitability of EP for WAS prior to AD was confirmed.

Improved anaerobic digestion performance of Miscanthus floridulus by different pretreatment methods and preliminary economic analysis

Suspended solids and residual oil removal in a liquid are relevant to numerous research areas and industry. The suspended solid cannot be removed completely by plain settling. Large and heavy particles can settle out readily, but smaller and lighter particles settle very slowly or in some cases do not settle at all. Because of this, it requires efficient physical-chemical pretreatment methods. Our current research is to study the pretreatment methods in the removal of suspended solids and residual oil content in POME. Preliminary analysis shows that POME contains 40,000 mg/L suspended solid and 4,000 mg/L oil and grease content that relatively very high compared to the maximum allowable limit by the Malaysian Department of Environment which are only 400 mg/L and 50 mg/L respectively. The methods chosen were coagulation-sedimentation method for suspended solids removal and solvent extraction for residual oil removal. Jar test apparatus was used as the standard procedure for bench-scale testing and alum was used as the coagulant. Parameters studied were alum dosage, mixing time, mixing speed, sedimentation time and pH. For removal of residual oil, six different organic solvents; n-hexane, n-heptane, benzene, petroleum ether, pentane and petroleum benzene were used. For every solvent the effect of solvent ratio, mixing time, mixing speed and pH were analyzed. The results show that the optimum conditions in removal of suspended solid from POME were at pH 4.11, sedimentation time of 100 minutes and 150 rpm mixing speed with 1.5 hr mixing time. N-hexane give the best performance in extracting residual oil from POME with solvent to POME ratio of 6:10. It was estimated about 0.54 grams of oil and grease can be extracted with optimum variables at pH 4, mixing speed of 200 rpm, and 20 minutes mixing time. Key Words: palm oil mill effluent, coagulation, suspended solid, residual oil, solvent extraction.

Changes in inorganic and organic matters in processed water from hydrothermal-treated biogas slurry

Long-term effect of free ammonia pretreatment on the semi-continuous anaerobic primary sludge digester for enhancing performance: Towards sustainable sludge treatment

This paper provides a comprehensive review of hybrid waste‐to‐energy (WTE) systems that integrate anaerobic digestion (AD) and biomass gasification, emphasizing their synergistic benefits in sustainable energy production and waste management. By combining biochemical and thermochemical processes, these hybrid systems maximize energy recovery, optimize resource utilization, and significantly mitigate environmental impacts. The study highlights the principles and operational dynamics of standalone AD and gasification technologies, showcasing how their integration addresses limitations such as incomplete biomass conversion and excessive digestate production. Hybrid systems demonstrate superior performance in converting diverse biomass feedstocks, including municipal solid waste (MSW), agricultural residues, and food waste, into renewable energy and valuable by‐products. Advancements in reactor designs, pretreatment techniques, and system configurations are discussed, with a focus on enhancing energy efficiency and reducing greenhouse gas (GHG) emissions. Pretreatment methods such as AD pretreatment and advanced sorting mechanisms are explored to address feedstock variability and improve process stability. Key synergies, such as utilizing waste heat from gasification to dry AD residues, further boost overall system efficiency. The paper identifies critical operational parameters such as feedstock composition and reactor conditions that influence system performance and explores emerging solutions. Economic and environmental benefits, such as improved energy yields and cost efficiency, demonstrate the potential of hybrid AD–gasification systems. Despite the advantages, challenges persist, particularly in scaling hybrid systems and managing feedstock variability. Infrastructural limitations and the complexity of balancing AD and gasification processes remain significant barriers to widespread adoption. By reviewing existing research and case studies, this paper underscores the critical role of hybrid systems in achieving global renewable energy goals and sustainable waste management practices. Ultimately, hybrid AD–gasification systems offer a promising pathway for transitioning to cleaner energy systems, maximizing waste valorization, and supporting the global shift toward a circular economy.

Growth comparison of microalgae in tubular photobioreactor and open pond for treating anaerobic digestion piggery effluent

Solid wastes from domestic, industrial and agricultural sectors cause acute economic and environmental problems. These issues can be partly solved by anaerobic digestion of wastes, yet this process is incomplete and generates abundant byproducts as digestate. Therefore, cultivating mixotrophic algae on anaerobic digestate appears as a promising solution for nutrient recovery, pollutant removal and biofuel production. Here we review mixotrophic algal cultivation on anaerobic waste digestate with focus on digestate types and characterization, issues of recycling digestate in agriculture, removal of contaminants, and production of biofuels such as biogas, bioethanol, biodiesel and dihydrogen. We also discuss applications in cosmetics and economical aspects. Mixotrophic algal cultivation completely removes ammonium, phosphorus, 17β-estradiol from diluted digestate, and removes 62% of zinc, 84% of manganese, 74% of cadmium and 99% of copper.