Preliminary Assessment of Pyrolysis Biochar Derived from Milk/ Dairy Processing Sludge as a Potential Component of Fertilizers

Disposal of waste-activated sludge [dairy processing sludge, (DPS)] from wastewater treatment plants located in milk processing companies is an increasing concern. DPS is usually applied to farmlands in the vicinity of the dairy companies. This practice is becoming unsustainable due to uncontrolled nutrient loss and potential soil contamination. We propose to recover nutrients in the form of biochar. This paper examines the properties of biochars obtained from slow pyrolysis of DPS. DPS samples were pyrolyzed at laboratory and pilot scale at 600 and 700 °C. The elemental properties of biochars, the content of primary and secondary nutrients, as well as contaminants were examined and compared against the European Union Fertilizing Products Regulation. The biochars meet the specified limits for hydrogen-to-organic carbon ratio, chloride, and polycyclic aromatic hydrocarbons intended for gasification and pyrolysis component category materials. In six out of eight biochars, the content of phosphorus (P) as a single declared nutrient and the level of contaminants meet those required for an organo-mineral fertilizer. Only two biochars meet the required concentrations of nitrogen, phosphorus, and potassium. A minimum solid content of 30% in DPS is required to make the process of biochar production energetically sustainable </p

Phosphorus recovery from hydrothermal carbonization of organic waste: a review

Background: This review sheds light on the topic of phosphorus (P) recovery from hydrothermal carbonization (HTC) of organic waste.The paper focuses on the rising need for securing alternative P sources for the increasing demand, in addition to the development of HTC as a thermochemical technique for waste valorization. Results: This article studies the definition of P-recovery from HTC, while introducing the notion of availability, which is a significant factor for studying the efficiency of P-recovery. A brief comparison between different treatment techniques for P-recovery from waste streams is presented, and the advantages of HTC are highlighted among different thermochemical techniques. Furthermore, the mechanisms of P-transformation during HTC reactions are studied, and the effect of various parameters on P-destination and recovery is emphasized. Finally, applications of P-recovery from HTC products on the laboratory and industrial scales are studied to assess the feasibility of the application. Conclusion: In short, the paper offers a detailed insight into the definition, mechanism, and potential feasibility of P-recovery from HTC of organic wastes within the scopes of resource management, waste valorization, and fertilizer production. Even though HTC for P-recovery from organic waste has been applied on laboratory and industrial scales, several challenges persist towards optimizing this process. The paper concludes that adopting P-availability as a criterion for efficiency is necessary to optimize HTC conditions for P-recovery. Further studies on P-transformation during later-stage reactions of HTC are recommended, as well.</p

Hydrothermal carbonization of milk/dairy processing sludge: Fate of plant nutrients

Dairy processing sludge (DPS) is a byproduct generated in wastewater treatment plants located in dairy (milk) processing companies (waste activated sludge). DPS presents challenges in terms of its management (as biosolids) due to its high moisture content, prolonged storage required, uncontrolled nutrient loss and accumulation of certain substances in soil in the proximity of dairy companies. This study investigates the potential of hydrothermal carbonization (HTC) for recovery of nutrients in the form of solid hydrochar (biochar) produced from DPS originating from four different dairy processing companies. The HTC tests were carried out at 160 ◦C, 180 ◦C, 200 ◦C and 220 ◦C, and a residence time of 1h. The elemental properties of hydrochars (biochars), the content of primary and secondary nutrients, as well as contaminants were examined. The transformation of phosphorus in DPS during HTC was investigated. The fraction of plant available phosphorus was determined. The properties of hydrochar (biochar) were compared against the European Union Fertilizing Products Regulation. The findings of this study demonstrate that the content of nutrient in hydrochars (biochars) meet the requirements for organo-mineral fertilizer with nitrogen and phosphorus as the declared nutrients (13.9–26.7%). Further research on plant growth and field tests are needed to fully assess the agronomic potential of HTC hydrochar (biochar).</p

Emissions modeling of fluidised bed co-combustion of poultry litter and peat

Gaseous emissions from the fluidised bed co-combustion of 50% w/w chicken litter and peat were monitored and recorded. Emission data were used to create a dispersion model for a proposed site on a poultry farm in Ireland. Variables within the combustion unit influenced both combustion and emission levels of pollutants such as SO2 and NOx, CO. Concentrations of atmospheric pollutants decreased with use of the correct ratio between fluidising and secondary air. Dispersion modelling of combustion at a proposed poultry unit predicted that ground level concentrations for the set of emissions data would be below the limits and guidelines set by air quality standards

A comparative study of thermally and chemically treated dairy waste: Impacts on soil phosphorus turnover and availability using 33P isotope dilution

Dairy processing sludge (DPS) and DPS-derived secondary products such as struvite, biochar, hydrochar and ash (collectively known as SRUBIAS) are emerging as alternatives to fertilizers produced from mined rock phosphate. However, little is known about how these products affect soil P availability and daily P turnover rates.. A lack of such information prevents precision nutrient management planning using these products out on farms. This study used a novel isotope dilution technique (IPD) with 33P as a tracer to compare P turnover in soils amended with chemically (alum-treated DPS and struvite) and thermally (biochar, hydrochar, ash) treated DPS. Results showed that thermally treated products exhibited poor agronomic performance as P fertilizers, potentially inhibiting P availability when applied to soils. For example, a P deficient soil amended with hydrochar treatment at the highest application rates did not record a build-up of available P to agronomic target values. In ash and biochar treated P deficient soils, available P increased but only with very high application rates of 150 and 80 mg P kg −1. The application of these products as fertilizers could have negative implications for both environmental and agronomic goals. Conversely, chemically treated fertilisers demonstrated better agronomic performance. The same agronomic target value was reached with application rates of only 20 mg P kg −1 soil for DPS and 50 mg P kg −1 soil for struvite. However, the techniques deployed revealed that these products exhibited slower rates of available and exchangeable P build-up when compared with chemical fertilisers. This suggests that these bio-based alternatives require higher application rates or earlier application times compared to conventional chemical fertilizers. Regulations providing advice on P use in agricultural soils need to account for slower P turnover in soils receiving recycled fertilizers. The IPD technique is transferrable to all wastes to examine their performance as fertilizers.</p

Changes in phosphorus turnover when soils under long-term P management are amended with bio-based fertiliser

Understanding available phosphorus (P) turnover could improve sustainable P management. An isotope tracing 33P was used to measure daily P turnover rates and exchangeable P (E) in P deficient, balanced, and excess P soils from a long-term P site. Turnover under P deficient conditions was characterised by the lowest P flux predominantly from the available into the exchangeable P pools (P efflux). The P efflux in the P deficient soil was 3.7 ± 0.6 mg P/L day− 1 and the inverse flux (P influx) was 1.6 ± 0.4 mg P/L day− 1 . Turnover rates were more than twofold higher under P balanced and surplus conditions, exhibiting an equilibrium between influx and efflux rates. The contribution of abiotic processes to P turnover was predominant in the excess P soil, whereas biotic processes dominated turnover rates under P deficient conditions. Changes in P turnover were measured following application of single superphosphate (SSP) and dairy processing sludge (DPS). Both fertiliser types increased P turnover rates and availability across all soils. After SSP application, E values plateaued between 238 and 297 mg P/L regardless of initial P status. Slower P release from DPS was evidenced by a wider range of E values (97–160 mg P/L) with slower turnover. </p

Catalytic valorisation of biomass levulinic acid into gamma valerolactone using formic acid as a H2 donor: a critical review

This review sheds light on the catalytic valorisation of agroforestry biomass through levulinic acid and formic acid towards g-valerolactone and other higher-value chemicals. g-Valerolactone is produced by the hydrogenation of levulinic acid, which can be achieved through an internal hydrogen transfer reaction with formic acid in the presence of catalyst. By reviewing corresponding catalysts, the paper underlines the most efficient steps constituting an integrated sustainable process that eliminates the need for external H2 sources while producing biofuels as an alternative energy source. Furthermore, the review emphasizes the role of catalysts in the hydrogenation of levulinic acid, with special focus on heterogeneous catalysts. The authors highlighted the dual role of different catalysts by comparing their activity, morphology, electronic structure, synergetic relation between support and doped species, as well as their deactivation and recyclability. Acknowledging the need for green and sustainable H2 production, the review extends to cover the role of photo catalysis in dissociating H2-donor solvents for reducing levulinic acid into g-valerolactone under mild temperatures. To wrap up, the critical discussion presented enables readers to hone their knowledge about different schools and emphasizes research gaps emerging from experimental work. The review concludes with a comprehensive table summarizing the recent catalysts reported between the years 2017–2021.</p

Temporal changes in labile soil phosphorus pools in grassland receiving P recycled from dairy processing sludge

Replacing chemical fertilisers with recycled products will require new advice for phosphorus (P) use.. Emerging P fertilisers derived from dairy processing sludge (DPS) include products such as struvite and hydrochar. A field study monitored temporal changes in available, exchangeable, and Mehlich3 P pools in a P deficient grassland amended with DPS-derived hydrochar and struvite. Herbage P content and yields were compared with data from plots amended with a mineral P fertiliser. Regardless of fertiliser used, there was no statistical difference in dry matter yield. However, herbage P content varied depending on the fertiliser type. The optimal P content in herbage for cattle feed (0.3–0.4 %) was reached using struvite and mineral fertiliser. Application of struvites increased available, exchangeable, and Mehlich3 P, raising the available P levels to the agronomic optimal value for crop production (>5 mg L-1) within one month. In hydrochar amended plots, the optimal level of P was reached 4 months after fertilisation, at the end of the growing season. During the low growth or dormancy period, soil P levels decreased and remained low regardless of the treatment. In the struvite amended plots, available and exchangeable P pools recovered at the beginning of the second season. This effect was not observed in mineral fertiliser and hydrochar amended plots. A single application of struvite can replace mineral fertilisers supplying crops with P for more than one season. This needs to be reflected in the advice for growers to avoid excessive P application and legacy P deposition. </p

Contrasting phosphorus build‑up and drawdown dynamics in soils receiving dairy processing sludge and mineral fertilisers

Sustainable utilisation of waste from the food industry is required to transition to a circular economy. The dairy industry relies on high phosphorus (P) inputs and produces large quantities of P-rich dairy processing sludge (DPS). Recycling DPS into P fertilisers provides an opportunity to decrease the reliance on chemical P fertilisers. However, current soil nutrient management planning (NMP) is based on chemical P and does not account for recycled alternatives. A pot trial using a novel isotope pool dilution technique was used to describe build-up and drawdown cycles of P in soils fertilised with DPS. Changes in available, exchangeable, and Mehlich3 P (M3-P) pools were recorded over 36 weeks of grass growth. Results demonstrated that in the period of high P demand (12 weeks), these P pools were depleted. As crop growth and demand decreased, available P recovered through mobilisation of P from exchangeable P and M3-P reserves. DPS allowed available P to recover and build up to agronomic target levels after 24 weeks. Using DPS, build-up of available and exchangeable P was slower but P use efficiency was higher at stages of slow growth. Dairy waste created a more stable P pool which could be utilised by crops over a growing season indicating that NMP needs to account for this in the decision support for growers. Isotope studies revealed that extractive agronomic tests do not capture drawdown in P reserves.</p

Catalytic etherification of 5-hydroxymethylfurfural into 5-ethoxymethy-furfural over sulfated bimetallic SO4 2− /Al-Zr/KIT-6, a Lewis/Brønsted acid hybrid catalyst

.A series of mesoporous composites of SO4 2− /Al-Zr/KIT-6, with varied ratios of ZrO2 to Al2O3 and degrees of sulfation have been synthesized as an efficient, clean, facile and environmental-friendly nano-catalyst for the selective etherification of biomass-derived 5 hydroxymethylfurfural (HMF) to produce 5-ethoxymethylfurfural (EMF) as a biofuel candidate in a one pot process. Structure/property relationships of the catalyst have been determined and optimized in terms of EMF yield and HMF conversion. The resulting catalyst has been further tuned through tailored reaction conditions to produce an EMF yield of 89.8 % and HMF conversion of 99