Effects of limed manure digestate application in sandy soil on plant nitrogen availability and soil N2O emissions

Anaerobically-digested manure is frequently applied to agricultural soil to enhance plant growth and reduce the need for chemical fertilizers. This practice also stimulates microbial nitrogen transformations and often results in N2O emissions. A single mesophilic anaerobic digestion is insufficient for pathogen removal or inactivation and therefore, a post treatment is required for its stabilization and hygienization. Here, we examined the effects of limed manure-digestate as a nitrogen source for plant growth and on N2O emission compared with compost. A plant growth experiment was conducted in a sandy soil and N2O emissions were monitored throughout the experiment. Plants were irrigated with freshwater or liquid-N fertilizer. The combination of compost application and liquid-N fertilizer resulted in surface N2O fluxes over 0.7 ​mg ​m−2 d−1, which were correlated with ammonium concentration in the soil. The presence of N2O in the rhizosphere was only detected in compost-amended soil 2–10 days after plantation. A significantly-lower surface N2O flux of 0.4 ​mg ​m−2 d−1 was recorded with application of limed-digestate, probably due to its effects on nitrogen-transforming microorganisms. Both compost and limed-digestate enhanced plant growth, with a more distinct effect in the freshwater treatment. Our observations demonstrate that limed-digestate can be an efficient substitute for compost as it effectively supports plant growth with substantially-lower N2O emissions

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)

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

Thermochemical 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. (C) 2016 Elsevier Ltd. All rights reserved

Hydrothermal Processing of Multilayer Plastic Film for Cascaded Valorization of Nonrecyclable Waste

Mixed polymer plastics cannot undergo mechanical recycling, resulting in heterogeneous low-quality recycled products. Multilayered mulch film, used in agriculture, is an example of mixed polymeric product, as it usually contains a gas barrier polymer layer, which is different in composition compared to the outer layers. Thus, multilayered mulch films are considered nonrecyclable and landfilled. Hydrothermal processing (HTP) is an alternative solution for mixed plastic waste management. HTP is used here as a combined separation and treatment of a multilayer film. Low-density polyethylene (LDPE) film with a 20–25 wt % barrier layer of polyamide (PA) was treated with HTP, and analyses were performed for products in all phases (solid, liquid, and gas). After HTP, the inner PA layer had decomposed, and 22 ± 3 wt % of the original film was recovered as caprolactam monomer and similar compounds in the liquid phase. The remaining solid product, 80 ± 2 wt % of the original film, mainly comprises the LDPE fraction. Evaluation of its suitability for subsequent processing with pyrolysis and mechanical recycling was also demonstrated. This work indicates that HTP can valorize landfill-designated mixed polymer plastics and should be considered as a beneficial alternative for a circular plastic economy

Acid and alkali catalyzed hydrothermal liquefaction of dairy manure digestate and food waste

The objective of this study was to elucidate the effect of adding acid and alkali to hydrothermal liquefaction (HTL) of two waste biomass feedstocks: manure digestate and carbohydrate-rich food waste. HTL reactions were conducted at 300 °C for 60 min, with and without the addition of acid or base. We measured the quantity and characterized the quality of the three main HTL products: oil, aqueous and hydro-char. For both feedstocks, carbon recovery distributions had wide ranges among (1) biocrude oil (26–61 wt %), (2) aqueous product (9–49 wt %) and (3) hydro-char (1–36 wt %). The addition of acid affected HTL reactions for manure more than for food waste. For the aqueous phase, the addition of acid decreased the recovery of C1–4 carboxylic acids and increased the production of cyclic furan compounds. GC–MS analysis of the biocrude oil suggested that dehydration reactions were enhanced by adding acid to the HTL media. FTIR spectroscopy coupled with principal component analysis showed that hydro-char samples cluster according to acid-modified and base-modified reactions, based on distinct chemical structures. This study clarifies the role of pH during HTL and its effect on chemical pathways and carbon distribution among products