Evaluation of Biosolids and Biosolids Derived Biochar for Soil Improvement

Biosludge, a byproduct from municipal and industrial wastewater facilities, is a major point of focus as it comprises a large portion of the overall treatment plant costs and is a concern for safe disposal. Biosolids are produced from biosludge after additional treatment to reduce volatile organic matter (VOM) and harmful pathogens. The use of biosolids for agriculture is a cost-effective way to enhance soils nutrients and water retention. However, there is limitation for direct application of biosolids as it contains trace toxic elements and microorganisms. Biochar produced from biosolids by the pyrolysis process addresses these risks, but at the cost of reduced organic matter and nutrient availability. Therefore, this thesis provides a comparative study between the biosolids practice and biochar derived from biosolids practice on plant growth and water use efficiency.Industrial biosolids (GBS) were considered for biochar (BC) production at three different temperature conditions of 350, 450 and 550 °C under a heating rate of 5 °C.min-1 and hold time of 30 min. The physicochemical properties of biosolids and biochar were characterized by following different standard procedures and applied to Qatar sandy soil at two different loading rates, 0.5 and 1% for the pot test. Pot tests were conducted with duplicates at outdoors environmental temperatures averaging 35±5 °C using two Okra (Abelmoschus esculentus) seeds per pot. The pots were irrigated with 20 to 60 mL of tap water daily and rotated daily to avoid shading biases for a period of fifty-one days. Plant growth and health were assessed based on height of plant, leaf numbers, length and width of leaves, chlorophyll content, leaf stomatal conductance and soil water retention capacity.Application of GBS at a 1% application rate gave the greatest Okra plant growth, while 1% application rate of BC 450 °C to the soil showed the highest soil water retention capacity, and also had a good improvement of plant growth. Liquid fertilizer was added partway through the test due to suspected nutrient deficiency in biochar amendments. Even after this addition, the 1% GBS was more effective in improving plant growth with the highest final shoot and root biomass, root and shoot moisture and nutrient adsorption. For biochar amended pots, the 0.5 % application of BC 450 °C showed the best plant growth and plant nutrient uptake post-liquid fertilizer application. The above outcome demonstrated biosolids, as well as biochar produced from biosolid at 450 °C, are the good amenders for infertile soil to enhance agriculture productivity and reduce water stress.Biosolids’ characteristics depend on the wastewater and the treatment processes employed. Therefore, a comparative study was also conducted between industrial and municipal biosolids for cultivation of two plants, Okra (Abelmoschus esculentus) and green beans (Phaseolus vulgaris) seeds. Pots were filled with potting soil (PS) and either GBS or municipal biosolid (MBS), at three different application rates of 0% and 1% and 5%. Various properties of biosolids amended with potting soil (PS) were analysed. Two seeds were planted in each pot with four replicate pots in each condition.In this test using already nutrient-rich PS, the biosolids amendments had a slightly negative, though not statistically significant, impact on Okra and green beans plant growth. However, these two biosolids improved soil CEC and enhancing soil water retention capacity. Overall, this study demonstrated that biosolids are a good amendment for poor quality soils and should be prioritized over biochar application except where concerns exist over pollutant accumulation in soils, or for transport and storage needs. However, longer-term studies are recommended, particularly in fertile soils, as well as detailed studies of the relative health risks of the two materials.