Renewable adsorbents from the solid residue of sewage sludge hydrothermal liquefaction for wastewater treatment.

Solid residue from hydrothermal liquefaction (HTL) of nutrient rich feedstock presents a promising source to recover valuable nutrients, such as phosphorus, in the solid form. The present work shows for the first time the potential of utilizing the waste residue remaining after nutrients extraction from HTL of sewage sludge, as renewable adsorbents. A parametric study was undertaken to investigate the influence of chemical activation conditions (temperature, residence time, activation agent loading, washing after activation) on raw and partially demineralized HTL solids. Kinetic and equilibrium adsorption investigation was undertaken for the removal of methylene blue (MB) from aqueous solution. For comparison purposes, a commercial activated charcoal (AC) was used. Demineralization was found to have a significant influence in the adsorption capacity of the resultant adsorbents. Three adsorbents were found to follow the Langmuir adsorption model, while the acid washed demineralized adsorbent had higher adsorption capacity than AC and was found to follow the Freundlich adsorption model. The superior performance of the acid washed demineralized adsorbent was verified from the kinetic study where all adsorbents were found to best fit the pseudo-second order model. Adsorption capacities for MB at equilibrium were 367.1, 332.3, 297.4 and 87.6 mg/g, for acid washed demineralized adsorbent, AC, demineralized adsorbent, and raw adsorbent, respectively. Finally, the most promising adsorbents were assessed for their adsorption capacity to remove pharmaceuticals present in a real wastewater treatment effluent. Results indicated ultimate concentration for all targeted compounds below the detection limits for acid washed demineralized adsorbent, AC and demineralized adsorbent. Future implementation of HTL technology in wastewater treatment facilities, will not only provide an efficient way to valorize sewage sludge into bio-crude and nutrients, but can also enhance technology integration by providing the precursors for renewable adsorbents needed in tertiary treatment of wastewater.

Hydrothermal liquefaction of the brown macro-alga Laminaria saccharina: effect of reaction conditions on product distribution and composition.

The brown macro-alga Laminaria saccharina was converted into bio-crude by hydrothermal liquefaction in a batch reactor. The influence of reactor loading, residence time, temperature and catalyst (KOH) loading was assessed. A maximum bio-crude yield of 19.3 wt% was obtained with a 1:10 biomass:water ratio at 350 °C and a residence time of 15 min without the presence of the catalyst. The bio-crude had an HHV of 36.5 MJ/kg and is similar in nature to a heavy crude oil or bitumen. The solid residue has high ash content and contains a large proportion of calcium and magnesium. The aqueous phase is rich in sugars and ammonium and contains a large proportion of potassium and sodium.

Seasonal variation in the chemical composition of the bioenergy feedstock Laminaria digitata for thermochemical conversion.

To avoid negative impacts on food production, novel non-food biofuel feedstocks need to be identified and utilised. One option is to utilise marine biomass, notably fast-growing, large marine 'plants' such as the macroalgal kelps. This paper reports on the changing composition of Laminaria digitata throughout it growth cycle as determined by new technologies. The potential of Laminaria sp. as a feedstock for biofuel production and future biorefining possibilities was assessed through proximate and ultimate analysis, initial pyrolysis rates using thermo-gravimetric analysis (TGA), metals content and pyrolysis gas chromatography-mass spectrometry. Samples harvested in March contained the lowest proportion of carbohydrate and the highest ash and alkali metal content, whereas samples harvested in July contained the highest proportions of carbohydrate, lowest alkali metals and ash content. July was therefore considered the most suitable month for harvesting kelp biomass for thermochemical conversion to biofuels.