No abstract

Currently, sewage waste management is a serious environmental problem and one of the major growing concerns for urban areas all over the world. Utilization of biosolids (BS) for crop production may be a sustainable waste management strategy. The present study evaluated the physico-chemical and biological characteristics of biosolids from sewage ponds at Egerton University, Kenya. This was to determine its suitability for crop production. Biosolids were evaluated separately then as mixture with forest soil at rates of 0, 10, 20, 30, 40, 50 and 60% and compared with tea compost (TC) and coco peat (CP) in a completely randomized design experiment with four replications. Data collected included: macro-elements, micro-elements, heavy metals, pH, electrical conductivity (EC), bulk density (BD), water holding capacity and biological properties. Results showed that total organic carbon (0.03%), total organic nitrogen (2.0%) and Molybdenum (22 mg kg-1), in biosolids were significantly (p < 0.05) higher compared with forest soil, but not significantly different from tea compost. For heavy metals, Hg (0.33 mg kg-1), As (5.9 mg kg-1), Cr (31.1mg kg-1), Cd (0.38 mg kg-1), Ni (16.3 mg kg-1) and Zn (127 mg kg-1) were significantly (p < 0.05) higher in biosolids but within the allowable limits according to Environmental Protection Agency (EPA) standards. bulk density (1.2 to 1.5) g cm-3 and pH (5.4 to 5.8) units, but high organic matter (195 to 230) g kg-1, water holding capacity (35 to 42 %) and EC (2.6 to 5.4) µSm-1). For microbial load, total viable count (TVC) and colony forming units (CFU) registered 5 ×10-7 and 6.5×10-7 respectively. However, Escherichia coli, Salmonella sp. and Staphylococcus sp. were not detectable in the fully composted biosolids. Similar trend of these results were subsequently observed in the substrates formed in the mixture of biosolids and forest soil and this provide insight on the potential of biosolids as substrate for crop production and a reliable alternative to soil alone.

Studies on the effects of biosolids (BS) amended substrate on food quality and safety in tomato production have not been adequately addressed. The objective of this study was to investigate the influence composted BS and NPK fertilizer in forest soil on post-harvest quality and safety of potted greenhouse tomatoes. Potted tomatoes ‘Maxim F1’were grown in a randomized complete block design with four replications. Inorganic fertilizer NPK fertilizer was applied at 0, 100 and 200 kg ha-1; BS was applied at 0%, 10%, 20%, 30%, and 40% v/v, in all possible combinations. Tomato were harvested and analyzed for ascorbic acid, chlorophylls, carotenoids and total phenolic compounds; weight loss, fruit firmness, titratable acidity  and total soluble solids, as well as heavy metals and microbial contaminants. Results revealed that tomato fruit at 10% BS in combination with NPK fertilizer at 100 kg ha-1had highest β-carotene (6.1 mg 100 g-1), lycopene (26.1 mg 100 g-1), ascorbic acids (128.0 mg 100 g-1), total phenolic acids (13.2 mg 100 g-1), total soluble solids (17%). However, the same rates produced tomato fruits with lower titratable acidity (2.2%) and had heavy metal residues within the permissible level, according to International EPA standards on biosolids utilization on food crops production. Similarly, no trace of targeted bacteria; Salmonella, Escherichia coli, Staphylococcus was observed on the ready to eat tomato. This study reveals BS 10% with NPK fertilizer at 100 kg ha-1 substrate as a better option of plant nutrient source for quality and safe greenhouse tomato production.