Abstract
Agricultural wastes, such as rice straw (RS) and pig manure (PM), cause serious environmental pollution due to the non-existence of effective disposal methods. Urgent investigations are needed to explore how such wastes can be transformed into resources. In this study, we comprehensively assessed methane yield and kinetics of RS and PM anaerobic co-digestion, with or without pretreatment of a previously developed cellulolytic microflora, under conditions of their maximum organic loading rate. The anaerobic co-digestion results revealed that the cumulative methane production of RS and PM after bio-pretreatment was 342.35 ml (g-VS)−1, which is 45% higher than that of the control group [236.03 ml·(g-VS)−1]. Moreover, the kinetic analysis showed the first-order kinetic, while the modified Gompertz models revealed higher fitting properties (R2 ≥ 0.966). After bio-pretreatment, the hydrolytic constant, maximum accumulative methane production, and maximum methane production rates of RS and PM reached 0.46 day−1, 350.79 ml·(g-VS)−1, and 45.36 ml·(g-VS)−1·day−1, respectively, which were 77, 45.1, and 84.3% higher than those without pretreatment. Also, we found that the lag phase and effective methane production time after bio-pretreatment decreased from 2.43 to 1.79 days and 10.7 to 8.92 days, respectively. Upon energy balance evaluation, we reported a net energy output of 5133.02 kWh·ton−1 after bio-pretreatment. Findings from this present study demonstrated that bio-pretreatment of RS and PM mixtures with cellulolytic microflora could greatly enhance methane production and anaerobic digestion efficiency.
Highlights
As a traditional agricultural country, nearly 29.69 million hectares of land in China is under rice production
0.9 g of CaCO3, 5.0 g of NaCl, 5.0 g of peptone, 1.0 g of yeast extract, 1.8 g of pig manure (PM), and 1 L of water were added to activate the cellulolytic microflora, which was isolated from decaying straw and silt in nature and the filter paper could be completely decomposed at 55◦C under 40 h of incubation by secreting cellulose-binding proteins (CBPs) (Zhang et al, 2011a, 2016)
The cumulative methane production of rice straw (RS) and PM was recorded at 342.35 ml·(g-volatile solids (VS))−1, which was a 45% increase, while the biodegradation increased by 45.06%
Summary
As a traditional agricultural country, nearly 29.69 million hectares of land in China is under rice production. In 2019, for instance, the rice output was 209.61 million tons (National Bureau of Statistics, 2019). With the large-scale development of pig farming in China, the environmental pressure brought by pig manure (PM) is gradually increasing (Wang et al, 2018). RS and PM are regarded as two types of typical agricultural wastes causing environmental pollution owing to the lack of efficient disposal measures. Most of these wastes were processed either into feedstuffs or fertilizers (Qian et al, 2014); their utilization efficiencies remained relatively low. There is an urgent need to explore new approaches to improve the utilization efficiency of these agricultural wastes
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