• Energy Research

With the rapid growth in population and urbanization, sustainable disposal of sewage sludge has become a prominent problem worldwide. Therefore, an adequate treatment is required to reduce the environmental impacts created from traditional methods such as incineration, landfill, etc. In this context, sewage sludge was liquefied hydrothermally under sub-supercritical conditions with and without catalyst (K2CO3). The effect of temperature and alkali catalyst on product distribution was investigated. Obtained results showed that the temperature had a negligible influence, whereas catalyst slightly improved the bio-crude yield and quality for both sub-supercritical conditions (350 and 400 °C). Bio-crude contained N-containing compounds, ketones, phenols, acids, and long-chain hydrocarbons. Carbon and nitrogen recoveries revealed that 58–67% of the carbon went into bio-crude, while the majority of the nitrogen was transferred to the aqueous phase. ICP-AES analysis indicated that approximately 80% of the heavy metals were concentrated in the solid phase. The leaching action of citric acid with sewage sludge not only removed 40% of ash content but also reduced 38% of the fat content.

Heavy metals (HMs) are undoubtedly an unavoidable nuisance in today's era, and their appropriate handling anddisposal carry the utmost significance. Construction wood (CW), specifically hazardous and non-hazardous woodis contaminated due to a mixture of different materials like paints, coatings, and copper layers, etc. that needproper attention for safe disposal. Wood waste from building and urban waste streams is abundantly available,which essentials to manage appropriately for energy recovery. In that respect, this study focused on the disposaloption of contaminated wood waste via hydrothermal liquefaction (HTL) by turning waste into biocrude. CW iscategorized into four types named Untreated wood (UNW), Non-hazardous wood (NHZW), Hazardous wood(HZW), and Mixed wood (MXW). Maximum biocrude yield was obtained by the liquefaction of UNW followed byNHZW, HZW, and MXW in the range between 24.86 and 36.35 wt%. Additionally, the fate of selected heavymetals (chromium, copper, nickel, zinc) was investigated in HTL products. It was concluded that, by the liquefactionof CW, the majority of HMs shifted to the solid residue. The negligible amount of HMs merged intothe biocrude and aqueous phase. This study suggests HTL as a promising and sustainable route for the disposal ofcontaminated wood waste by turning into higher added value (or high quality) products especially biocrude withless HMs concentration as a fruitful product at large scale.

Intense farming activities and the growth of the population produce increasing amounts of wastes, which represent an environmental concern and require an adequate disposal. Animal manure, fish sludge, and sewage sludge are all wet wastes consisting of organic, but also inorganic material. Hydrothermal liquefaction is proposed to treat these wastes as wet feedstocks can be processed without any drying. The organic fraction is valorized, being converted into biocrude oil, while the inorganics are recovered primarily in the solid products. The decomposition of these wastes is investigated under sub- (350 °C) and supercritical (400 °C) conditions, and with and without the addition of K2CO3 catalyst with focus on the biocrude yield and quality. High yields of biocrude are obtained from the liquefaction of all the feedstocks, especially from fish sludge (ca. 50% d.a.f.) and sewage sludge (ca. 45% d.a.f.). A reduction in biocrude production is observed at supercritical conditions for animal wastes, however, the quality of manure-derived biocrudes is improved when using supercritical conditions and by the addition of the catalyst. Carbon is primarily recovered in the biocrude: 50–60% for swine and cow manure, 55–80% for fish and sewage sludge. Considerable quantities of nitrogen and sulfur are transferred to the biocrude, respectively 26–60% and 33–66%. Most of the inorganics (e.g. Ca, Mg, P) are recovered in the solids (above 70%), except for potassium and sodium, which show a higher degree of solubility in the aqueous phase.

The management and optimization of the aqueous phase are the major challenges that hinder the promotion of hydrothermal liquefaction (HTL) technology on a commercial scale. Recently, many studies reported about the accumulation of the N-content in the bio-crude with continuous recycling of the aqueous phase from high protein-containing biomass. In the present study, sewage sludge was processed at 350 °C in an autoclave. The produced aqueous phase was treated with activated carbon, and its subsequent recycling effect on the properties of the bio-crude and aqueous phase was investigated. By contacting the aqueous phase with activated carbon, 38–43% of the total nitrogen was removed from the aqueous phase. After applying the treated aqueous phase recycling, the energy recovery of the bio-crude increased from 50 to 61% after three rounds of recycling. From overall carbon/nitrogen recoveries, 50 to 56% of the carbon was transferred to the bio-crude phase and more than 50% of the nitrogen remained in the aqueous phase. The aqueous phase contained mostly of N&O-heterocyclic compounds, small chain organic acids, and amides. ICP-AES analysis showed that more than 80% of the inorganic elements were concentrated into the solid phase.

In the present study, eucalyptus biomass was processed to produce biocrude via hydrothermal liquefaction.

Corrosion of concrete sewer pipes caused by hydrogen sulphide is a problem in many sewer networks. The mechanisms of production and fate of hydrogen sulphide in the sewer biofilms and wastewater as well as its release to the sewer atmosphere are largely understood. In contrast, the mechanisms of the uptake of hydrogen sulphide on the concrete surfaces and subsequent concrete corrosion are basically unknown. To shed light on these mechanisms, the uptake of hydrogen sulphide from a sewer gas phase was compared to the biological hydrogen sulphide removal potential of the concrete corrosion products. The results showed that both microbial degradation at and sorption to the concrete surfaces were important for the uptake of hydrogen sulphide on the concrete surfaces.