Abstract
The utilization of chemical fertilizers on crops results in negative effects on wetlands, lakes, and rivers due to fertilizer runoff. The high nutrient content in chemical fertilizers promote eutrophication which consume the amount of oxygen in the water and result in death to aquatic system. This work seeks to demonstrate manufacturing of organic fertilizers from biomass waste and wastewater sludge to increase soil fertility and food production without intoxicating the soil by using composting method. This method retains good microorganisms found in the soil and contributes towards bioremediation to reduce negative effects in groundwater.
The optimized parameters such as: appearance, pH, conductivity, particle size, moisture content, odor, impurities, matrix, stability, and maturity displayed appearance of black-ish and dark-brown color, possessing a smell like forest soil, smooth in texture, homogenous mixture and moisture content conformed to hand-squeeze test. The compost reached a stability alkaline pH of 8.30.
The morphological properties of the compost were determined using scanning electron microscope which indicated sharp shiny and dark materials which represented the heavy metals present in the compost. The EDS mapping showed a range of detected elements in the compost at a different composition, salts such as sodium and aluminum were also detected at the highest concentration.
Department of Agriculture Forestry and Fisheries, denotes product or (compost) minimum nutrient content of different organic fertilizers such as (sewage sludge, chicken manure and cow dung) are none specific in terms of nitrogen, phosphorus, and potassium. The specified nutrient content (fluoride) acceptable level is (400.0 mg/L), all raw samples (cow manure, chicken manure, dry sludge, wet sludge) and the other three composts contained low concentrations of fluorine (0.1570-63.30 mg/L) below the detection limit.
Bioremediation process (Bacillus species and Aspergillus Niger) was applied for removal or reduction of contaminants such as heavy metals (Nickel, Copper, Lead, Cadmium and Zinc while Aspergillus Niger from fungal group will be used to remove Copper, Lead, Cadmium and Nickel. ICP –OES was used to quantify the concentration of heavy metals in the compost.
The performance evaluation of the compost was determined in assisting to grow plants in water and soil of known quality. The plantation of tomato and spinach leaves showed a shorter germination period in treated compost compared to untreated soil. Growing mint plant in compost showed green healthy thick leaves with pest and disease resistance as compared to plant growing in water only with burnt looking yellowish-leave edges.
Microbial analysis of compost showed presence of B cereus, lactic acid and S. aureus bacteria and absence of E coli. The virgin soil and plant products indicated the absence of fecal contamination.
The spinach leaves were found to be safe to eat, having concentration of heavy metals detected such as Cr (2.513 mg/L) and Pb (2.063 mg/L) were above the acceptable limits set by Food and Agricultural Organization/World Health Organization standard with below acceptable limits set by Indian standard. The developed composting method (for converting wastewater sludge and food biomass into a fertilizer) will be applied in Tshwane municipality to produce the organic fertilizers in a large quantity for community development. This will contribute towards food growth and community development.