Quadratic response models for N and P mineralization in domestic sewage sludge for mininig dump reclamation

• Response surface methodology as suitable tool to model soil nutrients mineralization.
• Mineralization model is an easy alternative to forecast the fate of sludge nutrients.
• Sludge co-composted was better as regards nutrient economy and release of bioelements.

A valuable feature of sewage sludge used for restoring degraded soils is its supplying capacity for C, N and P. A series of laboratory incubation experiments to quantify the release of N and P from raw (dried) and co-composted urban sewage sludges applied to mine dump soil were conducted. The effect of application dose (0–100 g kg−1) and incubation time (0–30 day) on N and P mineralization as well as the process modelling were carried out by Response Surface Methodology. Models fitted revealed significant interaction effects between factors involved in soil-sludge dynamics, which accounted for 26% total variance in N-mineralization. The response models were used to predict nutrient releases required in properly formulating sludge management guidelines, viz. maximum simultaneous value for extractable inorganic forms of N and P achieved 11 and 18 days after applying 100 g kg−1 of co-compost and dried sludge, respectively. Addition of sludges resulted into mineralization of 18% total N and up to 15% total P, while chemical and biochemical properties of the amended soil were improved paralleling organic matter mineralization. Compared to dried sludge, co-composting sludge lead to a decline of up to 30% and 65% in the availability in soil of N and P, respectively, but at expenses of C losses of only 7%, illustrating that co-composting was superior in turning sludge into an environmentally safe soil amendment.