Biocrude extraction from human-excreta-derived hydrochar for sustainable energy and agricultural applications.

Hydrothermal carbonization may be a sustainable sanitary treatment for wet organic waste including human excreta. Human-excreta-derived hydrochar properties differ from those of typical wet biomass due to the formation of a biocrude-like phase at low reaction temperatures. This study characterized the importance of this phase in terms of hydrochar combustion properties and potential agricultural use. Hydrothermal carbonization of raw human excreta was undertaken at 180, 210, and 240 °C, after which the biocrude phase was extracted with dichloromethane. Physicochemical properties, surface-area parameters, combustion profiles, and gas emissions of non-extracted hydrochar, biocrude, and extracted hydrochar were compared. The potential agricultural use of extracted hydrochar was assessed in germination experiments. Biocrude comprised up to 49.5% of hydrochar mass with a calorific value of >60% that of extracted hydrochar. Biocrude combustion properties were better than those of hydrochar, before and after extraction as demonstrated by higher combustion index value (Si). The extracted hydrochar surface area (34.7 m2 g-1) was greater than that of non-extracted hydrochar (<2 m2 g-1), and seeds germinated more readily due to the lower phytotoxin content. Most macro and micronutrients required for plant growth were retained in the extracted hydrochar. The extraction of biocrude from human-excreta-derived hydrochar not only provided a higher-quality fuel with enhanced combustion properties but also improved hydrochar characteristics, suggesting its potential as a soil additive for enhanced plant growth.

Repurposing anaerobic digestate for economical biomanufacturing and water recovery.

Due to mounting impacts of climate change, particularly increased incidence of drought, hence water scarcity, it has become imperative to develop new technologies for recovering water from nutrient-rich, water-replete effluents other than sewage. Notably, anaerobic digestate could be harnessed for the purpose of water recovery by repurposing digestate-borne minerals as nutrients in fermentative processes. The high concentrations of ammonium, phosphate, sulfate, and metals in anaerobic digestate are veritable microbial nutrients that could be harnessed for bio-production of bulk and specialty chemicals. Tethering nutrient sequestration from anaerobic digestate to bio-product accumulation offers promise for concomitant water recovery, bio-chemical production, and possible phosphate recovery. In this review, we explore the potential of anaerobic digestate as a nutrient source and as a buffering agent in fermentative production of glutamine, glutamate, fumarate, lactate, and succinate. Additionally, we discuss the potential of synthetic biology as a tool for enhancing nutrient removal from anaerobic digestate and for expanding the range of products derivable from digestate-based fermentations. Strategies that harness the nutrients in anaerobic digestate with bio-product accumulation and water recovery could have far-reaching implications on sustainable management of nutrient-rich manure, tannery, and fish processing effluents that also contain high amounts of water. KEY POINTS: • Anaerobic digestate may serve as a source of nutrients in fermentation. • Use of digestate in fermentation would lead to the recovery of valuable water.

Subcritical water extraction as a circular economy approach to recover energy and agrochemicals from sewage sludge.

Global population growth is creating severe pressure on wastewater treatment plants, and specifically on sludge management. Meanwhile, the global challenge of achieving food-security requires the development of green pest control practices that maximize crop productivity. The hydrothermal technology, using subcritical water as the conversion media has been intensively studied, mostly for energy recovery purposes. Here, we focused on the aqueous phase by-product of this process and studied the subcritical water extraction of sewage sludge to recover valuable agrochemicals, with high potential of pre-emergent herbicidal activity. Full characterization of hydrothermal extracts from different reaction temperatures (200-300 °C) and times (30-120 min) highlighted the formation of pyrazine derivatives. Seed germination bioassays with three different species suggested a positive correlation between reaction temperature and extract herbicidal activity. Moreover, differences in seed viability and final root elongation between the tested crop (Trriticum aestivum) and weeds (Lapidium sativum and Amaranthus palmeri) may indicate the competitive abilities that can play a key role in weed management. Our results suggest that subcritical water can be applied as a green solvent for extracting a valuable agrochemical from sewage sludge and improving the circular economy for wastewater treatment.

Integrated biological treatment of fowl manure for nitrogen recovery and reuse.

Biowaste such as animal manure poses an environmental threat, due to among others, uncontrolled emissions of ammonia and additional hazardous gases to the atmosphere. This study presents a quantitative analysis of an alternative biowaste management approach aimed at nitrogen recovery and reduction of contamination risks. The suggested technology combines anaerobic digestion of nitrogen-rich biowaste with biofiltration of the resulting gaseous ammonia. A compost-based biofilter is used to capture the ammonia and convert it to nitrate by nitrifying microorganisms. Nitrogen mass balance was applied to quantify the system's capacity under various fowl manure-loading regimes and ammonia loading rates. The produced nitrate was recovered and its use as liquid fertilizer was evaluated with cucumber plant as a model crop. In addition, emissions of other hazardous gases (N(2)O, CH(4) and H(2)S) were monitored before and after biofiltration to evaluate the efficiency of the system for treating these gases. It was found that nitrate-rich liquid fertilizer can be continuously produced using the suggested approach, with an over 67 percentage of nitrogen recovery, under an ammonia loading rate of up to 40 g NH(3) per cubic meter biofilter per hour. Complete elimination of NH(3), H(2)S, CH(4) and N(2)O was achieved, demonstrating the potential of the suggested technology for mitigating emission of these gases from fowl manure. Moreover, the quality of the recovered fertilizer was demonstrated by higher yield performance of cucumber plant compared with control plants treated with a commonly applied organic liquid fertilizer.

Phosphorus recycling from waste activated sludge using the hydrothermal platform: Recovery, solubility and phytoavailability.

To address the grand challenge of increasing the sustainability of wastewater treatment plants, hydrothermal carbonization was studied as a nutrient recovery platform, transforming sludge into a valuable hydrochar. Carbonization was achieved at different temperatures (200-300 °C) and durations (30-120 min). The highest mass recovery (73%) was observed in the lowest temperature, while the lowest (49%) was obsereved at the highest temperature. Under all reaction conditions, phosphorus recovery values exceeded 80%, with the dominated fraction of inorganic-P in the hydrochar being HCl-extractable. Although HCl-extractable P is considered a moderately labile P fraction, P phytoavailability assays indicate that sewage sludge hydrochar is an excellent source for P, surpassing soluble P, likely due to its slow-release nature. We postulate that polyphosphates constitute a significant portion of this P pool. Overall, we emphasize the benefits of using HTC as a circular economy approach to convert sludge into a valuable hydrochar.

Hydrothermal processing of polyethylene-terephthalate and nylon-6 mixture as a plastic waste upcycling treatment: A comprehensive multi-phase analysis.

Accumulation of plastic waste is harming eco-systems and it is time to move towards a circular plastic economy. Sustainable production and recycling processes for plastics are challenged mostly by the lack of renewable building blocks. This study investigates hydrothermal processing (HTP) as a platform for depolymerization of two commonly used plastic polymers. Subcritical water (300 °C; 10 MPa) was tested as a solvent to treat polyethylene terephthalate (PET) and nylon-6 individually and in a mixture for a short reaction time of 90 min. Monomer recovery, gaseous emissions, and the effect of polymer mixture were evaluated by comprehensive analyses of all reaction products. Terephthalic acid (TPA), one of two monomers of PET was recovered as a solid product with a mass yield of 75%. ε-caprolactam (CPL), the single monomer of nylon-6 was recovered as a liquid product with a mass yield of 92.5%. Following PET + nylon-6 co-processing, TPA recovery decreased by 20%, whereas CPL recovery was not affected. Since TPA and CPL were recovered in different phases, an easy separation can likely be created for co-processing of PET and nylon-6. While most HTP studies neglect analysis of the gas phase, acetaldehyde and cyclopentene emissions were detected during HTP of PET and nylon-6, respectively. As shown here, gaseous emissions, which may be toxic, should be addressed in future developments of HTP for plastics. The results presented here can contribute to developing HTP processes for plastic recycling, that will be part of a circular plastic economy and a more sustainable future.

Hydrothermal carbonization of anaerobic digestate and manure from a dairy farm on energy recovery and the fate of nutrients.

Hydrothermal carbonization (HTC) of raw and anaerobically digested (AD) manure with either water or whey was studied, with the goal of recovering energy and nutrients. Specifically, the impacts of HTC reaction temperature (180-240 °C), solid feedstock, and type of liquid on hydrochar quality and aqueous phase properties were tested. Of the hydrochars produced, the calorific value of whey-based hydrochar was the highest, (19.4 and 16.0 MJ/kg for manure and digestate, respectively). Overall, the net energy gain was higher for HTC of manure with whey (7.4-8.3 MJ/kg dry feedstock) and water (4.4-5.1 MJ/kg) compared to the combined AD-HTC process with whey (4.4-5.3 MJ/kg) and water (2.3-2.9 MJ/kg). Digestate-derived hydrochar contained up to 1.8% P, higher than manure-derived hydrochar (≤1.5%). Using whey as a liquid for HTC increased the aqueous-phase N-P-K concentrations up to 3,200, 410, and 7,900 mg/L, respectively, suggesting its potential use as a liquid fertilizer.

Granular sludge is a preferable inoculum for the biochemical methane potential assay for two complex substrates.

The biochemical methane potential (BMP) assay is a standard method for characterizing biomethane potential and anaerobic biodegradability organic waste streams. Therefore, the BMP protocol must be standardized to reliably compare these parameters for various substrates. Here, the effect of inoculum selection on biomethane potential was investigated through BMP tests using two different substrates and inocula obtained from four different anaerobic digesters. It was found that inocula in the form of granular sludge yielded overall higher biomethane potential and generally had faster kinetics than suspended biomass. Furthermore, acclimation of inocula to substrate appeared to have little effect on degradation rates, and co-inoculation (with both suspended and granular biomass) did not perform better than single inoculation (e.g., with suspended sludge alone). These results emphasize the role of granular sludge as an preferable inoculum for BMP assay.

Combining anaerobic digestion and hydrothermal liquefaction in the conversion of dairy waste into energy: A techno economic model for New York state.

There is increasing global interest and policies being enacted to lower greenhouse gas emissions, especially from the agricultural sector. In the U.S. for example, states with large dairy operations may combine proven manure valorization technologies, such as anaerobic digestion and hydrothermal liquefaction. Sustainable manure treatment would increase the recovery of energy and other useful co-products, namely biogas, biocrude oil and hydro-char as well as lower the environmental impacts. In this study, the economic feasibility of implementing a centralized bioenergy system in New York State was investigated. The feasibility of this transformation depends on many factors, including capital costs, discount rates, and other financing arrangements, electricity selling prices, incentives and farm sizes and locations. For a large-scale implementation in New York State accounting for nearly 50% of the state's dairy farms, our model of a distributed, hybrid anaerobic/hydrothermal system was shown to treat 590 million liters of wet manure per day, producing 607 million kWh of electricity, 162,000 L of biocrude oil and 117,000 kg of hydro-char per day. Electricity selling price is a critical factor. Increasing the electricity selling price from wholesale ($0.06/kWh) to retail ($0.18/kWh) increased the net present value from $395 million to $1.5 billion (considering a 40-year project lifetime).

Coupling hydrothermal liquefaction and membrane distillation to treat anaerobic digestate from food and dairy farm waste.

Increased demand for water, energy and food requires new ways to produce fertilizers, fuels and reusable water. Recovery of resources from wastes could lead to an additional source of energy and nutrients, and also reduce the waste to be disposed. In this work, we used hydrothermal liquefaction to produce a biocrude oil product, followed by membrane distillation of the aqueous effluents to concentrate a nutrient-rich stream that can be used as fertilizer. The motivation for this work is that residual heat from the hydrothermal liquefaction process could be utilized to drive the membrane distillation process, which would improve the efficiency and reduce the cost of the distillation process. The membrane distillation system was demonstrated to be able to recover 75% of the water. The membrane distillation retentate had very high ammonium and phosphate concentrations, making it suitable as a fertilizer. Membrane permeate contained high concentrations of volatile organics.

Integrating electrochemical, biological, physical, and thermochemical process units to expand the applicability of anaerobic digestion.

Anaerobic digestion (AD) is a mature biotechnology-production platform with millions of installations at homes, farms, and industrial/municipal settings. Large-scale industrial, agricultural, and municipal waste-treatment systems may observe novel integration with electrochemical, biological, physical, and thermochemical process units to make AD more attractive. Without governmental subsidies, AD has often only a relatively low economic return or none at all. Diversification of products besides methane in biogas may help to change this. Here, several sections discuss different process units to: 1) upgrade biogas into biomethane; 2) convert carbon dioxide in biogas to more biomethane; 3) generate cooling power from process heat; 4) produce bio-crude oil (bio-oil) from organic matter; and 5) produce a liquid biochemical product from organic matter. This is not meant to be an exhaustive list, but rather a selection of particularly promising process units from a technological view, which are already integrated with AD or close to full-scale integration.

Seasonal and soil-type dependent emissions of nitrous oxide from irrigated desert soils amended with digested poultry manures.

Expansion of dryland agriculture requires intensive supplement of organic fertilizers to improve the fertility of nutrient-poor desert soils. The environmental impact of organic supplements in hot desert climates is not well understood. We report on seasonal emissions of nitrous oxide (N2O) from sand and loess soils, amended with limed and non-limed anaerobic digestate of poultry manure in the Israeli Negev desert. All amended soils had substantially higher N2O emissions, particularly during winter applications, compared to unammended soils. Winter emissions from amended loess (10-175mgN2Om-2day-1) were markedly higher than winter emissions from amended sand (2-7mgN2Om-2day-1). Enumeration of marker genes for nitrification and denitrification suggested that both have contributed to N2O emissions according to prevailing environmental conditions. Lime treatment of digested manure inhibited N2O emissions regardless of season or soil type, thus reducing the environmental impact of amending desert soils with manure digestate.

Coupling hydrothermal liquefaction and anaerobic digestion for energy valorization from model biomass feedstocks.

Hydrothermal liquefaction converts food waste into oil and a carbon-rich hydrothermal aqueous phase. The hydrothermal aqueous phase may be converted to biomethane via anaerobic digestion. Here, the feasibility of coupling hydrothermal liquefaction and anaerobic digestion for the conversion of food waste into energy products was examined. A mixture of polysaccharides, proteins, and lipids, representing food waste, underwent hydrothermal processing at temperatures ranging from 200 to 350°C. The anaerobic biodegradability of the hydrothermal aqueous phase was examined through conducting biochemical methane potential assays. The results demonstrate that the anaerobic biodegradability of the hydrothermal aqueous phase was lower when the temperature of hydrothermal processing increased. The chemical composition of the hydrothermal aqueous phase affected the anaerobic biodegradability. However, no inhibition of biodegradation was observed for most samples. Combining hydrothermal and anaerobic digestion may, therefore, yield a higher energetic return by converting the feedstock into oil and biomethane.

Prospects for energy recovery during hydrothermal and biological processing of waste biomass.

Thermochemical and biological processes represent promising technologies for converting wet biomasses, such as animal manure, organic waste, or algae, to energy. To convert biomass to energy and bio-chemicals in an economical manner, internal energy recovery should be maximized to reduce the use of external heat and power. In this study, two conversion pathways that couple hydrothermal liquefaction with anaerobic digestion or catalytic hydrothermal gasification were compared. Each of these platforms is followed by two alternative processes for gas utilization: 1) combined heat and power; and 2) combustion in a boiler. Pinch analysis was applied to integrate thermal streams among unit processes and improve the overall system efficiency. A techno-economic analysis was conducted to compare the feasibility of the four modeled scenarios under different market conditions. Our results show that a systems approach designed to recover internal heat and power can reduce external energy demands and increase the overall process sustainability.

Phases' characteristics of poultry litter hydrothermal carbonization under a range of process parameters.

The aim of this work was to study the hydrothermal carbonization of poultry litter under a range of process parameters. Experiments were conducted to investigate the effect of HTC of poultry litter under a range of operational parameters (temperature, reaction time, and solids concentration) on the formation and characteristics of its phases. Results showed production of a hydrochar with caloric value of 24.4MJ/kg, similar to sub-bituminous coal. The gaseous phase consisted mainly of CO2. However, significant amounts of H2S dictate the need for (further) treatment. The process also produced an aqueous phase with chemical characteristics suggesting its possible use as a liquid fertilizer. Temperature had the most significant effect on processes and product formation. Solids concentration was not a significant factor once dilution effects were considered.