Effect of alkali solids amendment on sewage sludge aerobic composting and the potential of related products on infertile soil amelioration

Aiming to evaluate the influence of alkali solids amendment on the sewage sludge aerobic composting and to declare the potential of related composts on infertile soil amelioration, sewage sludge and sawdust mixture were amended with straw biochar, hardwood biochar, fly ash and lime by 10% addition ratio in dry weight during the aerobic composting process; finally, potential of the related composts on the infertile soil amelioration was investigated by pot experiment. The results showed that the alkali solids amendment could prolong the thermophilic phase, and promote the composting material heat inactivation. Addition of straw and hardwood biochar facilitated more than 21.65% and 18.16% organic matter degradation. During the composting, the compost pH decreased at the beginning and then gradually increased before reached values of 6.78-7.33, while the fly ash and lime amendments could lead to higher pH values in the beginning stage. The alkali solids amendment reduced the salinity of the compost with final products EC lower than 3000 μS·cm-1. The addition of straw and hardwood biochar could increase the total nitrogen content by reducing the ammonia loss at the beginning, while the fly ash and lime amendments would result in ammonia loss in the beginning stage. Despite the composting variation, the contents of nitrate increased and the ammonium salt content decreased gradually. The biochar addition can accelerate the nitrate transformation while the fly ash and lime amendment had slight inhibitory effect on the nitrate transformation and plant germination. The pot experiment revealed that applying compost products could significantly improve the brassica growth, Cu and Zn micronutrients accumulation since the compost addition could increase the soil organic carbon content, as well as soil N, P, and K contents. Compared with the non-amended compost, the alkali solids amendment could slightly reduce the Cu and Zn micronutrients accumulation, while the fertile potentials were acceptable. The study indicated that straw and hardwood biochar were more suitable than fly ash and lime as compost amendment, and the related compost products had great potential on infertile soil amelioration. © 2016, Science Press. All right reserved.