The compostability and direct land application of paper mill sludge.

Abstract

Mpact Ltd strives for the environmentally friendly disposal of waste material generated by 3 mills, Mill A, B and C. Mill C makes use of unbleached bagasse pulp to produce fluting and corrugated packaging paper, producing an effluent sludge stream (PMSC) and a stream which contains the pith waste (pith). It was in their best interest to investigate the land application of this pith/PMSC blend as a suitable disposal option. Hence the scope of this study was (i) the preliminary characterisation of the pith/PMSC blend, (ii) investigate the compostability of pith/PMSC blend and (iii)to investigate the effects on soil properties when applying raw pith/PMSC blend to soil. The nutrient value of this pith/PMSC blend had not yet been quantified hence Chapter Three covers the preliminary characterisation of all the PMS samples.It was concluded that the moisture content in all samples exceeded the desirable range for composting due to the mill specific dewatering equipment. In addition, an inverse relationship between pH and EC was observed. The nutrient availability was also found to be dependent on the pH. Chapter Four investigates the compostability of pith/PMSC on a small and a large scale using porous bags in each case. It was observed that the composting materials in both the small and large scale composting experiments did not rapidly heat up at the beginning. It was concluded that the moisture, air and the volume of the composting material were the key parameters responsible for this. The compostability experiments were, however, successful in producing an end product that was within the desired specifications and limits. The direct land application of pith/PMSC (3:1) on soils was investigated by analysing soils treated with pith/PMSC (3:1). The application was found to be beneficial to soil after seeing an improvement in cation exchange capacity and C/N ratio. It was concluded that more applications of this will be beneficial to the soil and crops in the long run and N immobilisation will be prevented. A laboratory scale experiment was done to assess the effect of pith/PMSC (3:1) on soil in a controlled environment using an ASTM standard method. This involved the aerobic degradation of varying ratios of pith/PMSC (3:1) mixed with soil in bioreactors, with constant monitoring of air flow, CO2 production and biodegradation rates. This part of the study, however, was inconclusive.The hypotheses of the study were correct as the pith/PMSCwas degraded by composting into a stable, environmentally friendly end product and the addition of pith/PMSC to soil as an amendment was beneficial to the soil.