This work pioneered the efficient coupling of a leach bed reactor (using a filter medium and no anaerobic sludge) and a continuous stirred-tank reactor (LBR-CSTR) to perform the anaerobic mono-digestion of pig manure. The leachate residue of the pig manure (LR-PM) was dried by a biodrying process. The results revealed that the LBR-CSTR (with ceramsite (C) as the filter medium) showed the best performance (the biogas production was 241.68 ml/g volatile solids (VS), which was 1.24 times higher than that of the control CSTR (CK)), the weight loss of pig manure was the highest (the reduction was 95.83%), and the organic degradation was 86.82% (which was 19.49% higher than that of the CK). The seed germination index (GI) was higher than 50%, and the clogging of the leach bed was overcome. The energy and resource utilizations of pig manure were readily achieved.

Introduction

Generally, the water content in the excreta of livestock and poultry without bedding is higher than 80%, and the water content is still high after solid and liquid separation. It is essential to adjust the water content to approximately 65% with bulking agents (Bernet and Beline, 2009
; Liedl et al., 2006) for compost. Unfortunately, Chinese bulking agents are limited and expensive because the material increases the cost. Anaerobic digestion technology is regarded as one of the most sustainable technologies due to its low energy consumption, high efficiency and new energy production in the process of treating livestock and poultry wastes (Holm-Nielsen et al., 2009). Traditional wet digestion (total solid content: 12%) mainly results in a large biogas liquid volume and serious secondary pollution. The high nitrogen content, significant ammonia inhibition and blockage of the single-phase reactor cause low biogas production. Recently, more than 60% of new biogas projects in Europe have adopted the high concentration/solid anaerobic digestion technology (Tricase and Lombardi, 2009; Yang et al., 2015), but the difficulty in stirring the solid digestion matter and the difficult mass and heat transfer processes, in addition to the accumulation of acidification, negatively impact the biogas production efficiency.