Pig slurry valorization by ammonia recovery, biogas upgrading and microbial protein production.

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Upcycling of nutrients from kitchen waste: Integration of anaerobic digestion system and microbial protein production system

Innovative technologies for biogas upgrading

Ammonia recovery from anaerobic digestate: State of the art, challenges and prospects

Australia is one of the major producers and exporter of agricultural products. Annually, Australian agriculture produces approximately 151 Tg CO2 equivalent emissions. The use of fossil fuels in crop cultivation, harvesting and transportation are considered as the primary source of these greenhouse gas (GHG) emissions. Moreover, agronomic management and crop residues left in the field also contribute to these GHG emissions. Alternative waste management practices include the use of crop residues and agro-wastes as feedstocks for bioenergy production. Anaerobic digestion is considered as sustainable environmental technology to convert industrial sugarcane residues to carbon dioxide (CO2) - neutral biogas. The biogas thus produced can be used to produce heat, electricity and upgrade to biomethane for vehicle use. The produced biomethane can replace the diesel consumption associated with GHG emission in cane transport. Sugarcane is one among the most cultivated crop in the world. Australia alone produced nearly 33.5 million tonnes of cane in 2018 (FAO 2018). These large production of sugarcane lead to an increase in crop residues and agro-wastes from the sugarcane industry. In this study, an investigation regarding the anaerobic co-digestion of crop residues and agro-wastes from sugarcane industry viz, sugarcane trash (SCT) or sugarcane bagasse (SCB) with chicken manure (CM) was investigated in a batch experiment at 37 °C. In spite of various researches conducted till date about co-digestion of lignocellulosic waste with manure, no research data was available regarding the effect of feed ratio on co-digestion of SCT/SCB with CM. This research gap was investigated in this study. In addition to this, steam explosion pre-treatment of SCT/SCB was included to investigate how the pre-treatment influence methane yield among different feed ratios of SCT/SCB with CM. At first, SCT and SCB were subjected to steam explosion pre-treatment (steam impregnation at 130 °C for 5 minutes followed by steam explosion). Later, two sets of biochemical methane potential (BMP) tests were conducted at an Inoculum to Substrate Ratio (ISR) of 2. Co-digestion of untreated and steam exploded SCT or SCB with CM was investigated at feed ratios of 75:25, 50:50 and 25:75 on volatile solids (VS) basis. Assays with 100% untreated and steam exploded SCT or SCB were also included. Chemical analysis revealed that the steam explosion improved the VS content in pre-treated biomass compared with untreated biomass. The increase in VS was 1.6% and 5.7% in SCT and SCB, respectively. On the other hand, a slight reduction in total solids (TS) of nearly 4% and 1% were observed in the case of SCT and SCB, respectively. BMP results showed that the steam explosion had a profound effect on the methane production rates and yields, especially for SCB than SCT. Methane (CH4) yields of 201.8 and 199 ml CH4/gVSadded were obtained during the mono-digestion of untreated SCT and SCB, respectively. The corresponding values for 100% steam-exploded SCT and SCB were 207.5 and 225.6 ml/gVSadded, respectively. In comparison to mono-digestion, the co-digestion of SCB or SCT with CM did not improve the methane yields. Nevertheless, pre-treatment improved the methane production rates and yields of pre-treated biomass than untreated biomass. Among the studied feed ratios, best methane yields of 206.5 ml/gVSadded were obtained when steam-exploded SCT was co-digested with CM at 75:25 ratio. However, methane yields decreased with an increase in the amount of CM added. SCB also showed a similar trend. The best methane yield of 199.5 ml/gVSadded was obtained when steam-exploded SCB was co-digested with CM at 75:25 ratio. Among the tested feed ratios, all co-digestion mixtures except for 75:25 and 50:50 ratios of untreated SCT to CM showed synergistic effects. The best synergistic effect of 18.57% was observed when untreated SCB was co-digested with CM at 25:75 ratio. Kinetic modelling results confirmed that the steam explosion pre-treatment improved the methane production rates and yields by increasing the hydrolysis rate constant values. However, a higher hydrolysis rate constant was noticed for SCT than SCB. The highest hydrolysis rate constant of 0.16 d-1 was achieved at feed ratios of 50:50 and 25:75 of pre-treated SCT:CM. Interestingly, more than 75% of methane in pre-treated assays was produced by Day 11. The study thus suggests that the steam explosion can improve the methane production rates, yields and productivity of SCT and SCB. However, the use of CM as co-substrate did not improve the methane yields when compared to the mono-digestion of SCT or SCB, but a positive synergism was evident in most of the co-digestion feed ratios.

SummaryAnaerobic digesters produce biogas, a mixture of predominantly CH4 and CO2, which is typically incinerated to recover electrical and/or thermal energy. In a context of circular economy, the CH4 and CO2 could be used as chemical feedstock in combination with ammonium from the digestate. Their combination into protein‐rich bacterial, used as animal feed additive, could contribute to the ever growing global demand for nutritive protein sources and improve the overall nitrogen efficiency of the current agro‐ feed/food chain. In this concept, renewable CH4 and H2 can serve as carbon‐neutral energy sources for the production of protein‐rich cellular biomass, while assimilating and upgrading recovered ammonia from the digestate. This study evaluated the potential of producing sustainable high‐quality protein additives in a decentralized way through coupling anaerobic digestion and microbial protein production using methanotrophic and hydrogenotrophic bacteria in an on‐farm bioreactor. We show that a practical case digester handling liquid piggery manure, of which the energy content is supplemented for 30% with co‐substrates, provides sufficient biogas to allow the subsequent microbial protein as feed production for about 37% of the number of pigs from which the manure was derived. Overall, producing microbial protein on the farm from available methane and ammonia liberated by anaerobic digesters treating manure appears economically and technically feasible within the current range of market prices existing for high‐quality protein. The case of producing biomethane for grid injection and upgrading the CO2 with electrolytic hydrogen to microbial protein by means of hydrogen‐oxidizing bacteria was also examined but found less attractive at the current production prices of renewable hydrogen. Our calculations show that this route is only of commercial interest if the protein value equals the value of high‐value protein additives like fishmeal and if the avoided costs for nutrient removal from the digestate are taken into consideration.

Biodegradable plastics, perceived as ‘environmentally friendly’ materials, may end up in natural environments. This impact is often overlooked in the literature due to a lack of assessment methods. This study develops an integrated life cycle impact assessment methodology to assess the climate-change and aquatic-ecotoxicity impacts of biodegradable microplastics in freshwater ecosystems. Our results reveal that highly biodegradable microplastics have lower aquatic ecotoxicity but higher greenhouse gas (GHG) emissions. The extent of burden shifting depends on microplastic size and density. Plastic biodegradation in natural environments can result in higher GHG emissions than biodegradation in engineered end of life (for example, anaerobic digestion), contributing substantially to the life cycle GHG emissions of biodegradable plastics (excluding the use phase). A sensitivity analysis identified critical biodegradation rates for different plastic sizes that result in maximum GHG emissions. This work advances understanding of the environmental impacts of biodegradable plastics, providing an approach for the assessment and design of future plastics.

Ammonia recovery from anaerobic digestion effluent by aeration-assisted membrane contactor

We have previously described a novel flow-electrode capacitive deionization (FCDI) unit combined with a hydrophobic gas-permeable hollow fiber membrane contactor (designated "CapAmm") and presented results showing efficient recovery of ammonia from dilute synthetic wastewaters (Zhang et al., Environ. Sci. Technol. Lett. 2018, 5, 43-49). We extend this earlier study here with description of an FCDI system with integrated flat sheet gas permeable membrane with comprehensive assessment of ammonia recovery performance from both dilute and concentrated wastewaters. The integrated CapAmm cell exhibited excellent ammonia removal and recovery efficiencies (up to ∼90% and ∼80% respectively). The energy consumptions for ammonia recovery from low-strength (i.e., domestic) and high-strength (i.e., synthetic urine) wastewaters were 20.4 kWh kg-1 N and 7.8 kWh kg-1 N, respectively, with these values comparable to those of more conventional alternatives. Stable ammonia recovery and salt removal performance was achieved over more than two days of continuous operation with ammonia concentrated by ∼80 times that of the feed stream. These results demonstrate that the integrated CapAmm system described here could be a cost-effective technology capable of treating wastewaters and realizing both nutrient recovery and water reclamation in a sustainable manner.

The removal and recovery of gaseous ammonia from poultry litter can benefit bird health and productivity and reduce environmental concerns of emissions from poultry production. We investigated the potential use of gas-permeable membranes as components of a new process to capture and recover ammonia in poultry houses. This process includes the passage of gaseous ammonia through a microporous hydrophobic membrane, capture with a circulating diluted acid on the other side of the membrane, and production of a concentrated ammonium salt. In bench-scale prototype testing using tubular expanded polytetrafluoroethylene (ePTFE) membranes and a 1 N acidic solution (sulfuric acid), the technology captured and recovered 96% of the ammonia lost from poultry litter. The recovery of ammonia could mimic the slow release during flock production or could be accelerated to a few days using hydrated lime amendments. The membrane manifolds can be placed close to the litter surface (above or below), reducing the exposure of the birds to ammonia. Considering that the ammonia is captured inside the houses, this technology could help reduce ventilation and energy needs to lower ammonia levels in poultry houses. The results obtained in this study show that the use of gas-permeable membrane technology could be an effective approach to recover ammonia from poultry litter. The final products are (1) cleaner air inside the poultry houses with benefits to bird health and reduced environmental emissions, and (2) a concentrated liquid nitrogen that can be re-used in agriculture as a valued fertilizer.

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

Microbial protein (MP) production by autotrophic hydrogen-oxidizing bacteria is regarded as a potentially sustainable approach to mitigate food crisis, water pollution, and climate change. Herein, a hybrid biological-inorganic (HBI) system which coupled energy-neutral ammonium recovery and in-situ upcycling for MP production was demonstrated. No energy and acids/bases were needed for ammonium recovery and pH control. The system was tested with different amounts of CO2 supply and operated at different operational modes (microbial fuel cell or microbial electrolysis cell mode). 0.381 g/L of biomass containing 64.79% of crude protein was produced using the recovered nitrogen and therefore led to 76.8% of ammonium recovery and 84.6% of COD removal from real municipal wastewater. The system although not yet optimal in terms of efficiency has a meaning in alleviating food crisis and environmental issues. Altogether, this study offers insight into developing an energy and resource-efficient power-to-protein process to supplement conventional food production globally.

Coupling electrochemical ammonia extraction and cultivation of methane oxidizing bacteria for production of microbial protein

Enhanced ammonia recovery from wastewater by a transmembrane electro-chemisorption system directly connecting anode chamber and cathode chamber with gas permeable membrane

Livestock manure is a major source of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O). The emissions can be mitigated by production of biogas through anaerobic digestion (AD) of manure, mostly together with other biowastes, which can substitute fossil energy and thereby reduce CO2 emissions and postdigestion GHG emissions. This paper presents GHG balances for manure and biowaste management as affected by AD for five Danish biogas scenarios in which pig and cattle slurry were codigested with one or more of the following biomasses: deep litter, straw, energy crops, slaughterhouse waste, grass–clover green manure, and household waste. The calculated effects of AD on the GHG balance of each scenario included fossil fuel substitution, energy use for transport, leakage of CH4 from biogas production plants, CH4 emissions during storage of animal manure and biowaste, N2O emissions from stored and field applied biomass, N2O emissions related to nitrate (NO3−) leaching and ammonia (NH3) losses, N2O emissions from cultivation of energy crops, and soil C sequestration. All scenarios caused significant reductions in GHG emissions. Most of the reductions resulted from fossil fuel substitution and reduced emissions of CH4 during storage of codigestates. The total reductions in GHG emissions ranged from 65 to 105 kg CO2-eq ton−1 biomass. This wide range showed the importance of biomass composition. Reductions were highest when straw and grass–clover were used as codigestates, whereas reductions per unit energy produced were highest when deep litter or deep litter plus energy crops were used. Potential effects of iLUC were ignored but may have a negative impact on the GHG balance when using energy crops, and this may potentially exceed the calculated positive climate impacts of biogas production. The ammonia emission potential of digestate applied in the field is higher than that from cattle slurry and pig slurry because of the higher pH of the digestate. This effect, and the higher content of TAN in digestate, resulted in increasing ammonia emissions at 0.14 to 0.3 kg NH3-N ton−1 biomass. Nitrate leaching was reduced in all scenarios and ranged from 0.04 to 0.45 kg NO3-N ton−1 biomass. In the scenario in which maize silage was introduced, the maize production increased leaching and almost negated the effect of AD. Methane leakage caused a 7% reduction in the positive climate impact for each percentage point of leakage in a manure-based biogas scenario.