Use of nanobubble water bioaugmented anaerobically digested sludge for high-efficacy energy production from high-solids anaerobic digestion of corn straw

Alleviation of propionic acid inhibition and enhancement of methane production in anaerobic digestion by micronano-bubble water supplementation

Micronano-bubble water (MNBW) was used to accelerate propionic acid (HPr) degradation and enhance methane production in anaerobic digestion (AD) in this study. Results showed that HPr degradation was accelerated by MNBW addition. Moreover, methane production was elevated by 13.5% to 18.4% under HPr inhibition by MNBW supplementation. Microbial analysis revealed that MNBW boosted the bacterial populations involved in protein and carbohydrate consumption. In addition, supplementation with MNBW improved the tolerance of archaea such as Methanosaetaceae to HPr inhibition, thus increasing methane production. MNBW also promoted alkalinity recovery, lowered intermediate alkalinity/partial alkalinity and volatile fatty acid/total alkalinity ratios, and enhanced buffering capacity. Enzyme activity increased by MNBW, including a 21.0% increase in coenzyme F420 and a 7.0% to 13.8% increase in extracellular hydrolase activity. This work highlights that MNBW is a promising approach to accelerate HPr degradation, optimize methanogenic pathways, and boost methane production.

Effects of nano-bubble water on anaerobic co-digestion of cabbage waste and cow manure under mesophilic and thermophilic conditions

The impact of four nano-bubble water (NBW) additions on the hydrolysis rate, methane yield, and microbial community of co-digestion of cabbage waste (CW) and cow manure (CM) under mesophilic and thermophilic conditions were investigated. Adding NBW under mesophilic conditions promoted hydrolysis, and the highest soluble chemical oxygen demand of the mesophilic digesters with the addition of CO2-NBW increased by 15.86%. Methane yield in the mesophilic digesters with Air-NBW and CO2-NBW increased by 17.54% and 14.72%, respectively. Moreover, the addition of NBW further accelerated the methane yield rate under mesophilic conditions. Due to the influence of thermophilic temperature, the impact of NBW addition on hydrolysis, methane yield, and methane yield rate in the thermophilic digesters did not differ significantly from the control. The addition of Air-NBW and N2-NBW in the thermophilic digesters resulted in only marginal increases in methane yield, by 1.09% and 5.61%, respectively. NBW addition enhanced both the abundance and diversity of microbial communities in both mesophilic and thermophilic digesters. The addition of NBW represents a promising technological advancement for enhancing the efficiency of anaerobic co-digestion of CW and CM.

Enhancement of alkaline pretreatment-anaerobically digested sludge dewaterability by chitosan and rice husk powder for land use of biogas slurry

Alkaline pretreatment can improve the methane yields and dewatering performance of anaerobically digested sludge, but it still needs to be coupled with other conditioning methods in the practical dewatering process. This study utilized four different flocculants and a skeleton builder for conditioning of alkaline pretreatment-anaerobically digested sludge. Chitosan was found to be the most effective in dewatering the sludge. Chitosan coupled with rice husk powder further improved the dewatering performance, which reduced normalized capillary suction time, specific resistance to filtration, and moisture content by 98.7%, 82.0%, and 12.1%. For land use of biogas slurry as a fertilizer, chitosan conditioning promoted the growth of corn seedlings, while the other three flocculants diminished the growth of corn seedlings. Chitosan coupled with rice husk powder further promoted the growth of corn seedlings by 103.5%, 65.0%, and 53.7% in fresh weight, dry weight, and root length, respectively. Overall, chitosan coupled with rice husk powder not only enhanced the dewaterability of alkaline pretreatment-anaerobically digested sludge but also realized the resource utilization of agricultural waste.

Synchronous improvement of methane production and digestate dewaterability in sludge anaerobic digestion by nanobubble

The subsequence anaerobic digestion (AD) of dewatered sludge (DWS) from wastewater treatment plants necessitates an emphasis on enhancing methane production and dewaterability. The effect of different nanobubble water (NBW) on AD of DWS was investigated under mesophilic conditions. Cumulative methane production was improved by 9.0-27.8% with the addition of different NBW (Air, CO2, He, and N2). NBW improved methanogenic performance by significantly enhancing the hydrolysis of sludge AD. Results from the digestate, the capillary suction time, specific resistance to filtration, and moisture content could be decreased by 14.6-18.2%, 18.8-29.6%, and 13.6-19.5%, respectively. The addition of NBW can improve the dewaterability of digestate by reducing the digestate particle size and increasing the zeta potential of digestate. The addition of NBW significantly increased methane production and improved dewaterability in AD; Air-NBW showed the best improvement.

Waste-to-energy barriers and solutions for developing countries with limited water and energy resources

The environmental risks of conventional waste disposal methods, along with the resource and energy value of waste, have formed the foundation for waste-to-energy (WtE) technology. WtE systems that work on recovering energy present a suitable solution to generate energy and sustainably manage waste. This type of waste management system in the Middle East and North Africa (MENA) region is still considered underutilized as WtE technology is rarely used due to a lack of experience in their specific local conditions, lack of qualified competencies, and the absence of an appropriate regulatory and legislative structure. This study reviews the existing WtE policies and regulations, and it investigates the potential of WtE techniques in the MENA region. Moreover, sustainability in water consumption is critical; therefore, various water-conservation techniques were reviewed and considered when selecting regulatory actions. The radiative sky cooling technique was recommended to reduce water consumption. Barriers to implementing WtE and solutions for developing countries were presented to enable proper WtE implementation.

Effects of chitosan and rice husk powder on thermal hydrolysis-anaerobic digested sludge conditioning: Dewaterability and biogas slurry fertility

To enhance the dewaterability of anaerobic digested sludge and to make full use of the biogas slurry. This study set up five sludge conditioning methods: polymeric ferric sulfate, polymeric aluminum chloride, cationic polyacrylamide, chitosan, and chitosan combined with rice husk powder. Their effects on the dewaterability of thermal hydrolysis-anaerobic digested sludge, bacterial community, and biogas slurry fertility were studied to find a non-toxic and non-risk dewatering technology for the environment and biogas slurry. Compared with that of the control group, moisture content, normalization capillary suction time, and specific resistance to filtration were reduced by 12.8%, 97.7%, and 82.9%, respectively. Chitosan enlarges the sludge flocs and forms complexes with proteins, disrupting the structure of the extracellular polymeric substances, thereby exposing more hydrophobic groups and reducing the hydrophilicity of the sludge. The subsequent addition of rice husk powder enhances the adsorption of hydrophilic substances and provides a stronger drainage channel for the sludge. In addition, the biogas slurry obtained by this conditioning method used as a fertilizer increased the dry weight and fresh weight of corn seedlings by 59.3% and 91.0%, respectively. And the total chlorophyll content increased by 84.6%. Pearson's correlation analysis showed that chitosan and rice husk meal had no toxic effect on the biogas slurry compared to the other three flocculants. The results showed that the combined treatment of chitosan and rice husk powder resulted in the best dewaterability. Overall, chitosan combined with rice husk powder is a green dewatering technology with great potential for anaerobic digested sludge dewatering and biogas slurry recycling.

Effects of food wastes based on different components on digestibility and energy recovery in hydrogen and methane co-production

This study was conducted for four organic fractions (carbohydrates, proteins, cellulose, lipids) at an inoculum concentration of 30 % and a total solid (TS) of 8 % to investigate the effect of the main components of food waste on the performance of the two-stage anaerobic digestion. The results showed that the gas phase products were closely related to the composition of the substrate, with the carbohydrate and lipid groups showing the best hydrogen (154.91 ± 2.39mL/gVS) and methane (381.83 ± 12.691mL/gVS) production performance, respectively. However, the increased protein content predisposes the system to inhibition of gas production, which is mutually supported by changes in the activity of dehydrogenase and coenzyme F420. Butyric acid (53.19 %) dominated the liquid phase products in both stages, indicating that all four organic fractions were butyric acid-based fermentation and that the final soluble chemical oxygen demand degradation reached 72.97 %-82.86 %. The carbohydrate and cellulose groups achieved the best energy recovery performance, with conversion rates exceeding 65 %. The above results can provide a useful reference for the resource utilization of food waste.

Navigating the waters of nixtamalization: Sustainable solutions for maize-processing wastewater treatment

Maize-processing wastewater, also known as nejayote, does represent a widespread residue originating from both small- and large-scale factories that produce maize-based products using the alkaline maize-cooking process (nixtamalization). Nejayote is a high-strength wastewater containing significant concentrations of soluble and insoluble organic and inorganic compounds resulting from the disintegration of maize, as well as from the substantial quantity of lime (Ca(OH)2) used in the process. In order to make nixtamalization more sustainable in terms of water usage and to mitigate the health and environmental issues related to nejayote discharges into environmental matrices and public sewage systems, appropriate and effective treatment processes must be applied either before effluent disposal or for water reuse purposes. With this problematic as the central topic, we conducted a comprehensive review of relevant literature addressing this issue spanning from the mid-1980s to the present day. This review covers three primary aspects: i) the extensive variability observed in the physicochemical composition of maize-processing wastewater, ii) the various biological and physicochemical methods developed for its treatment, and iii) the potential for organic and mineral resource recovery from this waste. Although initial efforts to treat nejayote were left behind for decades, recent years have witnessed a resurgence of research interest in these research topics mainly underpinned by the urgency to conserve water resources. Based on the comprehensive evaluation of the existing literature, we identified the existing limitations on nejayote treatment and identified prospects for developing robust and technically feasible treatment possibilities. Within this review, we propose three main approaches for wastewater treatment and water reuse: physicochemical-based technologies, bioprocess in tandem with membrane technology, and low-cost bioprocesses coupled to physicochemical methods.

Microbiome-functionality in anaerobic digesters: A critical review

Microbially driven anaerobic digestion (AD) processes are of immense interest due to their role in the biovalorization of biowastes into renewable energy resources. The function-versatile microbiome, interspecies syntrophic interactions, and trophic-level metabolic pathways are important microbial components of AD. However, the lack of a comprehensive understanding of the process hampers efforts to improve AD efficiency. This study presents a holistic review of research on the microbial and metabolic "black box" of AD processes. Recent research on microbiology, functional traits, and metabolic pathways in AD, as well as the responses of functional microbiota and metabolic capabilities to optimization strategies are reviewed. The diverse ecophysiological traits and cooperation/competition interactions of the functional guilds and the biomanipulation of microbial ecology to generate valuable products other than methane during AD are outlined. The results show that AD communities prioritize cooperation to improve functional redundancy, and the dominance of specific microbes can be explained by thermodynamics, resource allocation models, and metabolic division of labor during cross-feeding. In addition, the multi-omics approaches used to decipher the ecological principles of AD consortia are summarized in detail. Lastly, future microbial research and engineering applications of AD are proposed. This review presents an in-depth understanding of microbiome-functionality mechanisms of AD and provides critical guidance for the directional and efficient bioconversion of biowastes into methane and other valuable products.

Green and chemical-free pretreatment of corn straw using cold isostatic pressure for methane production

In this study, the effect of cold isostatic pressure (CIP) pretreatment on the physicochemical properties and subsequent anaerobic digestion (AD) performance of corn straw (CS) was explored. The CS was subjected to CIP pretreatment by pressures of 200, 400 and 600 MPa, respectively, while AD was carried out at medium temperature (35 ± 2 °C). The results showed that CIP pretreatment disrupted the dense structure of the CS and altered the crystallinity index and surface hydrophobicity of the CS, thereby affecting the AD process. The presence of CIP pretreatment increased the initial reducing sugar concentration by 0.11-0.27 g/L and increased the maximum volatile fatty acids content by 112.82-436.64 mg/L, which facilitated the process of acidification and hydrolysis of the AD. It was also observed that the CIP pretreatment maintained the pH in the range of 6.37-7.30, maintaining the stability of the overall system. Moreover, the cumulative methane production in the CIP pretreatment group increased by 27.17 %-64.90 % compared to the control group. Analysis of the microbial results showed that CIP pretreatment increased the abundance of cellulose degrading bacteria Ruminofilibacter from 21.50 % to 27.53 % and acetoclastic methanogen Methanosaeta from 45.48 % to 56.92 %, thus facilitating the hydrolysis and methanogenic stages. The energy conversion analysis showed that CIP is a green and non-polluting pretreatment strategy for the efficient AD of CS to methane.