The Controlled Eutrophication Process: Using Microalgae for CO2 Utilization and Agricultural Fertilizer Recycling

Due to its effectiveness and ease of application, the process of flocculation and coagulation is often used for pollution removal in wastewater treatment. Most of these coagulants precipitate and accumulate in waste activated sludge (WAS), and could negatively affect sludge treatments, as observed for anaerobic digestion. Nowadays, wastewater treatment plants (WWTPs) are widely discussed because of the current paradigm shift from linear to circular economy, and the treatments performed at the facility should be planned to avoid or reduce adverse effects on other processes. The aim of this study was to compare the impact of poly aluminum chloride (PAC) and aluminum sulfate (AS) on WAS anaerobic digestion, by feeding replicate serum reactors with different levels of coagulant (5, 10 and 20 mg Al/g TS). Reactors without the addition of any coagulants represented the control group. Results revealed that Al-based coagulants inhibited methane production, which decreased as the coagulant addition increased. The inhibition was much more severe in AS-conditioned reactors, showing average reductions in methane yield from 14.4 to 31.7%, compared to the control (167.76 ± 1.88 mL CH4/g VS). Analytical analysis, FTIR and SEM investigations revealed that the addition of coagulants affected the initial conditions of the anaerobic reactors, penalizing the solubilization, hydrolysis and acidogenesis phases. Furthermore, the massive formation of H2S in AS-conditioned reactors played a key role in the suppression of methane phase. On the other hand, the use of coagulant can promote the accumulation and recovery of nutrient in WAS, especially in terms of phosphorus. Our findings will expand research knowledge in this field and guide stakeholders in the choice of coagulants at full scale plant. Future research should focus on reducing the effect of coagulants on methane production by modifying or testing new types of flocculants.

Improving fermentative methane production of glycerol trioleate and food waste pretreated with ozone through two-stage dark hydrogen fermentation and anaerobic digestion

Food waste, among the organic wastes, is one of the most promising substrates to be used as a renewable resource. Wide availability of food waste and the high greenhouse gas impacts derived from its inappropriate disposal, boost research through food waste valorization. Several innovative technologies are applied nowadays, mainly focused on bioenergy and bioresource recovery, within a circular economy approach. Nevertheless, food waste treatment should be evaluated in terms of sustainability and considering the availability of an optimized separate collection and a suitable treatment facility. Anaerobic codigestion of waste-activated sludge with food waste is a way to fully utilize available anaerobic digestion plants, increasing biogas production, energy, and nutrient recovery and reducing greenhouse gas (GHG) emissions. Codigestion implementation in Europe is explored and discussed in this paper, taking into account different food waste collection approaches in relation to anaerobic digestion treatment and confirming the sustainability of the anaerobic process based on case studies. Household food waste disposal implementation is also analyzed, and the results show that such a waste management system is able to reduce GHG emissions due to transport reduction and increase wastewater treatment performance.

Biogas production from brown grease using a pilot-scale high-rate anaerobic digester

To accomplish the rapid start-up and stable operation of biogas digesters, an efficient inoculum is required. To obtain such an inoculum for food waste anaerobic digestion, we domesticated dairy manure anaerobic digestion residue by adding food waste every day. After 36 days, the pH and biogas yield stabilized signifying the completion of domestication. During domestication, the microbial communities in the inocula were investigated by constructing 16S rDNA clone libraries. We evaluated the effect of the domesticated inoculum by testing batch food waste anaerobic digestion with a non-domesticated inoculum as a control. The pH and methane yield of the digestion systems were determined as measurement indices. Domestication changed the composition and proportion of bacteria and archaea in the inocula. Of the bacteria, Clostridia (49.3%), Bacteroidales (19.5%), and Anaerolinaceae (8.1%) species were dominant in the seed sludge; Anaerolinaceae (49.0%), Clostridia (28.4%), and Bacteroidales (9.1%), in domestication sludge. Methanosaeta was the dominant genus in both of the seed (94.3%) and domestication (74.3%) sludge. However, the diversity of methanogenic archaea was higher in the domestication than in seed sludge. Methanoculleus, which was absent from the seed sludge, appeared in the domestication sludge (21.7%). When the domesticated inoculum was used, the digestion system worked stably (organic loading rate: 20 gVS/L; methane yield: 292.2 ± 9.8 mL/gVS; VS = volatile solids), whereas the digestion system inoculated with seed sludge failed to generate biogas. The results indicate that inoculum domestication ensures efficient and stable anaerobic digestion by enriching the methanogenic strains.

Anaerobic digestion has been up to now essentially applied to wastewater. However, anaerobic treatment of organic solid waste fits in well with the new requirements for waste management. The Valorga full-scale plant in Tilburg (the Netherlands) is designed to process 52,000 tons per year of organic municipal solid waste separately collected. The Valorga digestion process is a semi-continuous, high-solid, one-step, plug-flow type process. The main characteristic is the complete absence of any mechanical equipment inside the reactors. The waste to be treated consists of food and garden waste. The characterization of the waste stream revealed a seasonal fluctuation in quantity and quality, that was correlated with seasonal garden waste production. The methane yield is varying from 210 to 290 m3 STP per Mg of volatile solids. It is related to waste composition. During the slack winter period the waste contains proportionally more food waste that is more biodegradable than lignocellulosic garden waste. The biological process was stable based on volatile acidity, alkalinity and ammonia measurements in the effluent. The organic residue, after dewatering and storage under aerobic conditions, can be considered as soil conditioner.

Anaerobic digestion is a viable on-site treatment technology for rich organic waste streams such as food waste and blackwater. In contrast to large-scale municipal wastewater treatment plants which are typically located away from the community, the effluent from any type of on-site system is a potential pathogenic hazard because of the intimacy of the system to the community. The native concentrations of the pathogen indicators Escherichia coli, Clostridium perfringens and somatic coliphage were tracked for 30 days under stable operation (organic loading rate (OLR) = 1.8 kgCOD m(-3) day(-1), methane yield = 52% on a chemical oxygen demand (COD) basis) of a two-stage laboratory-scale digester treating a mixture of food waste and blackwater. E. coli numbers were reduced by a factor of 10(6.4) in the thermophilic stage, from 10(7.5±0.3) to 10(1.1±0.1) cfu 100 mL(-1), but regenerated by a factor of 10(4) in the mesophilic stage. Neither the thermophilic nor mesophilic stages had any significant impact on C. perfringens concentrations. Coliphage concentrations were reduced by a factor of 10(1.4) across the two stages. The study shows that anaerobic digestion only reduces pathogen counts marginally but that counts in effluent samples could be readily reduced to below detection limits by filtration through a 0.22 µm membrane, to investigate membrane filtration as a possible sanitation technique.

With rising energy demand and the need for sustainable waste treatment, anaerobic digestion (AD) has emerged as a key technology for converting organic residues into renewable energy. However, predicting methane yield in full-scale facilities remains challenging due to the complexity of AD processes, the variability of feedstocks, and the impracticality of frequent biochemical methane potential (BMP) testing. In this study, we developed a simple, data-driven approach to forecast methane production in a commercial-scale digester co-digesting manure and food waste. The model employs weekly cumulative BMP of feedstock mixtures, calculated from literature values, as the explanatory variable. The model achieved an R2 of 0.70 and a forecast mean absolute percentage error (MAPE) of 7.4, indicating its potential for full-scale AD prediction. Importantly, the analysis revealed a long-run equilibrium between BMP and methane yield, with deviations corrected within roughly one month—closely matching the system’s hydraulic retention time. These findings demonstrate that literature-based BMP values can be used to reliably predict methane yield in operating AD systems, offering a low-cost and scalable tool to support decision-making in waste management and biogas plant operations.

BACKGROUNDThe research and applications of anaerobic digestion (AD) in plateau areas are limited by the specific climatic conditions (e.g., low temperature, large temperature difference). To explore feasible and economical strategies of AD in these regions, the effects of different temperature modes (constant mode: 35, 25, 15 °C; stepwise changes mode that simulated daily environmental temperature changes: 35–25 °C, 25–15 °C) and substrate/inoculum (S/I) ratios (1: 1, 1: 2, 1: 4) on Tibetan food waste (FW) digestion performance and microbial community structure were analyzed. Besides this, the energy balance of AD under different conditions was estimated.RESULTSThe methane yields (335–463 mL g−1 VS) of FW at temperature changes mode with less energy consumption could reach the same level or even slightly higher than the methane yields at 35 °C. Kinetic analysis revealed that, compared with 25 °C, methane production performance was not greatly affected by temperature fluctuations around 25 °C. The relative abundance of acetoclastic methanogens (e.g., Methanosaeta) were dominant over hydrogenotrophic methanogens (e.g., Methanobacterium, Methanospirillum) at 35 °C. The opposite was true at 15 °C.CONCLUSIONThe decrease in temperature caused the digestion pathway to shift from acetoclastic to the hydrogenotrophic pathway. The effect of temperature on the microbial community structure was more pronounced than the S/I ratio. Energy balance calculations showed that psychrophilic conditions and AD without temperature control were likely to be more economically competitive than mesophilic conditions for small‐scale AD in cold regions. © 2021 Society of Chemical Industry (SCI).

This paper discusses the applicability of effluent reuse in agriculture after treatment in a series of anaerobic, facultative and maturation ponds. The WSP system is located in Ginebra municipality, a small town in southwest Colombia. The total HRT is 12 days. Several samples of the final effluent were taken over a 55 day period and were analysed for E. coli, Streptococcus spp. and helminth eggs. Some additional grab samples were taken to determine the presence of pathogenic bacteria such as Salmonella spp. and Shigella spp. The results showed that the system was able to remove 4 log units of E. coli, 1 log unit of Streptococcus spp. and 100% of helminth eggs. Meanwhile, Salmonella spp. were detected in the effluent of the facultative pond whilst Shigella spp. were not detected in any sample. The main species of helminth eggs encountered were Taenia spp., Ascaris spp., Trichuris spp., Hymenolepis nana, H. diminuta and Enterobius vermicularis. Removal efficiencies were satisfactory despite the relatively short HRT. Nevertheless, WHO guidelines were slightly surpassed in the case of E. coli for unrestricted irrigation. The helminth egg value was always below the maximum WHO limit. Hence, this effluent can be safely used for restricted irrigation provided that field workers are protected from direct contact with wastewater given the presence of Salmonella spp. in the facultative pond effluent.

Synergistic carbon-rich biomass adjustment and Acetivibrio thermocellus bioaugmentation to enhance hydrogen and methane production in two-phase anaerobic digestion of food waste.

Phycoremediation coupled production of algal biomass, harvesting and anaerobic digestion: Possibilities and challenges

This work investigated the potential of generating biogas from mono-digestion of various substrates such as food and fruit waste (e.g., durian shell, dragon fruit peel and pineapple peel) and co-digestion in different combinations of a co-substrate as food waste as well as different types of fruit waste (durian shell, dragon fruit peel and pineapple peel). The mixture of food waste and fruit waste ratio varied as follows: 75:25, 50:50 and 25:75, which was based on weight. The batch experiments were carried out using 125 ml anaerobic digesters and were incubated for 50 days. For a mono-substrate, food waste produced the highest amount of methane gas (60.63 ± 1.02 ml/gvs) followed by durian shell (34.93 ± 1.30 ml/gvs), pineapple peel (31.70 ± 1.60 ml/gvs), and dragon fruit peel (30.12 ± 1.20 ml/gvs), respectively. The highest amount of methane gas came from food waste mixed with durian shell (FW75:D25), and it was on a higher level than food waste mixed with dragon fruit peel (FW75:DF25) and pineapple peel (FW75:P25). The highest methane gas production of co-digestion which was observed at the proportion of food waste and durian shell was 75:25 and produced higher content of methane gas than the highest methane gas production of mono-digestion (food waste) according to the high organic compound and optimum pH value in the system. The results showed that the co-digestion of durian shell and food waste improved methane production and reduced the startup time compared with their mono-digestion. On the other hand, pineapple peel was not suitable for co-digestion with food waste due to a decreasing pH value in the system.

Livestock manure treatments have become a more serious problem because massive environmental pollutions such as green and red tides caused by non-point pollution sources from livestock manures have emerged as a serious social issue. In addition, more food wastes are being produced due to population growth and increased income level. Since the London Convention has banned the ocean dumping of wastes, some other waste treatment methods for land disposal had to be developed and applied. At the same time, researches have been conducted to develop alternative energy sources from various types of wastes. As a result, anaerobic digestion as a waste treatment method has become an attractive solution. In this study has three objectives: first, to identify the physical properties of the mixture of livestock wastewater and food waste when combining food waste treatment with the conventional livestock manure treatment based on anaerobic mesophilic digestion; second, to find the ideal ratio of waste mixture that could maximize the collection efficiency of methane (CH4) from the anaerobic digestion process; and third, to promote CH4 production by comparing the biodegradability. As a result of comparing the reactors R1, R2, and R3, each containing a mixture of food waste and livestock manure at the ratio of 5:5, 7:3, and 3:7, respectively, R2 showed the optimum treatment efficiencies for the removal of Total Solids (TS) and Volatile Solids (VS), CH4 production, and biodegradability.

The food waste hierarchy as a framework for the management of food surplus and food waste