Wastewater C : N ratio effects on soil hydraulic conductivity and potential mechanisms for recovery

To sustain the performance of a land treatment system, soil hydraulic condu ctivity must be maintained. Biological clogging of soil pores tends to decr ease hydraulic conductivity. The changes in soil biological properties and hydraulic conductivity were examined in repacked soil cores receiving weekl y additions of wastewater with three C:N ratios for 28 weeks. We tested whe ther addition of a nitrification inhibitor (dicyandiamide, DCD) and polysac charidase enzyme preparation (PEP) with wastewater would maintain hydraulic conductivity. Increases in wastewater C:N ratio increased soil microbial b iomass, carbohydrate, and nematode population and decreased nitrate leachin g and hydraulic conductivity, by up to 80%. While neither DCD nor PEP treat ments lowered soil carbohydrate, both had increased hydraulic conductivity (in the range of 280-290%) in cores irrigated with high C:N wastewater, rel ative to 'nil' treatment wastewater. (C) 1999 Elsevier Science Ltd. All rig hts reserved.