The removal of moisture and antibiotic resistance genes in dairy manure by microwave treatment
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RESEARCH ARTICLE
The removal of moisture and antibiotic resistance genes in dairy manure by microwave treatment Tao Luo 1,2 & Yi Wang 2 & Pramod Pandey 2 Received: 13 May 2020 / Accepted: 23 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract To characterize the drying of dairy manure during microwave (MW) heating, and to determine the impacts of microwave radiation on reductions of antibiotic resistance genes (ARGs), this study investigated on understanding the effects of microwave heating on solid streams of flushed dairy manure. A series of experiments were performed to determine the rate of drying, moisture removal percentages, change in solids, and the level of ARGs. Manure was exposed to microwave radiation for 30–300 s at a frequency of 2450 MHz. The results showed moisture removal rate (U) up to 0.63-g water per minute per gram of dairy manure. During MW treatment, volatile solid (VS) content was relatively stable. The MW treatment resulted in reduction of ARGs such as sulII, intI1, and tnpA. The ARG concentrations (sulII, intI1, and tnpA) were reduced by 2 orders of magnitude in less than 1 min of microwave heating. The preliminary results of this study showed that MW treatment can be a viable option for drying of dairy manure and reducing ARGs in manure. Keywords Microwave drying . Drying kinetics . Antibiotic resistance genes . Energy consumptions . Moisture removal
Introduction Enormous amount of dairy manure is produced in dairy farms that requires disposal in an environmentally responsible way to protect ambient water and air. In the USA alone in 2019, there were over 94 million cattle that generated billions of tons of manure in a year (USDA-NASS 2020). Manure treatment methods such as anaerobic digestion are used to control greenhouse gas emissions from dairy manure and renewable energy (such as biogas) production by utilizing dairy manure as feedstocks (Qian et al. 2020; Pandey et al. 2011; Costa et al. 2017). Another method such as composting of dairy manure is used to treat manure and produce soil amendment for crop land (Hou et al. 2018; Cai et al. 2019; Pandey et al. 2016). While both composting and anaerobic digestion processes are used for treating dairy manure, composting is mainly used for Responsible editor: Diane Purchase * Pramod Pandey [email protected] 1
Biogas institute of ministry of agriculture and rural affairs, Chengdu 610041, Sichuan, China
2
Department of population health and reproduction, Veterinary medicine school, University of California, Davis, CA 95616, USA
treating solid streams of dairy manure and anaerobic digestion is used for treating liquid streams of dairy manure. Solid and liquid manure streams are produced in a dairy farm where flush system is used for removing feces from barn areas (Pandey et al. 2018). To separate solid from liquid slurry, mechanical solid–liquid separation systems are used, which can produce solid streams of manure with 12–14% of solids and liquid streams with 2–4% of solid (Hjorth et al. 2011; Khalil
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