• Energy Research

Phosphorus presents a limited, irreplaceable and essential nutrient necessary for the growth of organisms. There is an increasing effort to recover phosphorus from production waste streams. Sewage sludge presents an important source of phosphorus but also contains organic pollutants and heavy metals. Thermal treatment technologies seem to be a promising option to treat sewage sludge and obtain ash/char from which high recovery rate of phosphorus can be reached. In this review, sewage sludge management options in compliance with EU legal requirements are first reviewed. Follows, an overview of sewage sludge thermal treatment technologies including incineration, hydrothermal carbonisation, pyrolysis and gasification, for the purpose of phosphorus recapture. We summarize recent advances in thermal treatment processes of sewage sludge and phosphorus recovery, identify challenges and knowledge gaps. Thermochemical methods proved to have many advantages over pure wet chemical methods for phosphorus recovery. The review provides the foundation for future research aimed at achieving efficient, economic and environmental sustainable recapture of phosphorus from sludge thermal treatment products.

The land disposal of waste from the poultry industry and subsequent environmental implications has stimulated interest into cleaner and more useful disposal options. The review presented here details advances in the three main alternative disposal routes for poultry litter, specifically in the last decade. Results of experimental investigations into the optimisation of composting, anaerobic digestion and direct combustion are summarised. These technologies open up increased opportunities to market the energy and nutrients in poultry litter to agricultural and non-agricultural uses. Common problems experienced by the current technologies are the existence and fate of nitrogen as ammonia, pH and temperature levels, moisture content and the economics of alternative disposal methods. Further advancement of these technologies is currently receiving increased interest, both academically and commercially. However, significant financial incentives are required to attract the agricultural industry.

Abstract A light commercial road vehicle fitted with a heated fuel line and tank was run on cold pressed and filtered camelina sativa seed oil and unheated mineral diesel fuel. It was found that the seed oil produced a maximum power at the road wheels of 43.25 kW and returned 12.57 km/l compared to 38.50 kW and 14.03 km/l for the mineral fuel. At an engine speed >2000 rpm and high loading, both smoke opacity and CO emitted from the exhaust was found to be approximately 50% lower with the seed oil than with the mineral fuel, however, NO was higher for the seed oil by almost 6% at engine speeds >3500 rpm, but similar 2 and O 2 emissions were similar and NO 2 emitted was negligible for both fuels. The effect of heating at 170 °C on the camelina sativa seed oil was investigated and a significant increase in viscosity was observed which coincided with a reduction in the iodine value of the oil.

Abstract Batch hydrothermal carbonization (HTC) experiments were carried out using dissolved air flotation (DAF) dairy sludge in order to investigate the effects of changing temperature, residence time and water-sludge ratio on the yield and quality of the products. The highest solid hydrochar (HC) yield of 84 % (dry basis) and highest HC energy yield of 96 %, were achieved at a temperature of 250°C, a residence time of 4h and a water content of 96 wt.%. The wt.% of carbon and corresponding energy yield of HC increased with process severity while the oxygen and volatile matter contents decreased. Similarly, HC ash content and ash elemental composition increased and the resulting solid became more stable and hydrophobic. The majority of the compounds detected in the liquid product were acids, with carbon chain ranging between C1 and C10. The total acid-phenol concentrations increased with the severity of the HTC operating conditions, but remained around 2500 ppm. The hydrocarbon content of the gaseous product was low and a high CO2 concentration was observed, while H2S concentration increased significantly with the increase in temperature, residence time and water content. A degradation mechanism for proteins and fats was developed and a full elemental mass balance was performed.

There is an increasing realisation that biomass and organic wastes are valuable feedstocks for second generation biorefining processes that give rise to platform chemicals to substitute for dwindling petrochemical resources, and for pyrolysis processes that produce syngas, bio-oil, and biochar from biomass, organic wastes, and the biorefining residuals of the future. The experimental work described has focused on physical properties and compositions of biochars produced from miscanthus (Miscanthus × giganteus), willow (Salix spp) and pine (Pinus sylvestris) at 500°C and at 400, 500, and 600°C in the case of the miscanthus. Although the morphologies of the cell structures were maintained in the pyrolysis, the surface area of the miscanthus biochar was greatly increased by heating at 600°C for 60 min. Nuclear magnetic resonance spectra showed the disappearance of evidence for the carbohydrate and lignin plant components as the pyrolysis temperature was raised, and the compositions of miscanthus biochars after heating for 10 and for 60 min at 600°C were very similar and composed of fused aromatic structures and with no traces of the aliphatic components in the starting materials. In greenhouse and growth chamber experiments the growth of maize (Zea mays L) seedlings was found to be inhibited by soil amendments with biochar from miscanthus formed at 400°C for 10 min, but stimulated by miscanthus char formed at 600°C for 60 min. In the course of discussion the relevance of the results obtained is related to the roles that soil amendments with biochar can have on soil fertility, carbon sequestration, on the emissions of greenhouse gases from soil, on fertilizer requirements, and on waste management. It is clear that biochar soil amendments can have definite agronomic and environmental benefits, but it will be essential to have clear guidelines for biochar production from various feedstocks and under varying pyrolysis parameters. It will be equally important to have a classification system for biochars that clearly indicate the product compositions that will meet acceptable standards. A case can be made for sets of standard biochars from different substrates that meet the required criteria.

Abstract This paper examines poultry litter (PL) as a resource in fuel quality terms and illustrates how the small scale application of fluidised bed technology solves both energy and waste problems, while producing a nutrient rich ash. PL was found to have a higher heating value (HHV) of 18 GJ t −1 on a dry basis (db). On an as received basis (ar), it had an ash mass fraction of 9% and the elemental phosphorous content of the ash was 110 g kg −1 . The resultant mineral matter can be utilised as a nutrient substitute for mineral fertiliser.

Energy recovery from pig manure offers an opportunity for waste utilisation and financial benefit. Samples of the solid fraction of separated pig manure and samples which had undergone chemical or biological pretreatment prior to separation were pyrolysed. A beech wood sample was pyrolysed for comparison. The chemically pre-treated and anaerobically digested materials had similar properties and showed similar behaviour during thermogravimetric analysis. However, the energy content of the gas arising from pyrolysis in a batch reactor at 600 °C comprises about 30% of the original energy of the feedstock in the case of the anaerobically digested materials and double that of the chemically pre-treated material. Therefore, the overall energy balance showed a loss of 595.9 MJ/t for the pyrolysis of the chemically pre-treated manure, while very small positive values of 351.7 MJ/t, 817.3 MJ/t and a significant value of 8935 MJ/t were found for anaerobically digested sample, un-pretreated solid and for wood, respectively.

In this study, hydrochars were prepared by hydrothermal carbonisation (HTC) of poultry litter (PL) at temperatures between 150-300°C with residence times of 30, 120 and 480min. The effects of treatment temperature and residence time on the yield and composition of hydrochar were investigated. Both treatment temperature and residence time effects were observed however, the effect of residence time was lower. The results indicated that the HHV was improved by up to 25.17% and the overall ash in hydrochar was significantly lower compared to PL, however this coincided with a lower hydrochar yield.