Retraction:Evaluation of Co-Digestion at a Commercial Dairy Anaerobic Digester

Abstract

Co-digestion of dairy manure with off-farm waste has become a common practice on US farms, however, little data at a commercial-scale is present within the literature. In response, a mesophilic, mixed plug-flow reactor co-digesting 16.36%v/v food processing substrates with dairy manure, was monitored for its performance and substrate effects. Co-digestion, as compared to substrate or manure-only digestion, allowed for more preferred levels of key micronutrients, neutral pH, and additional alkalinity while also producing C/N and C/N/P ratios of 28:1 and 112:4:0.5, respectively. Reduction percentages were 45.36, 55.28, 67.72, and 99.87% for TS, VS, COD, and VFA, respectively, while fecal coliform bacteria as an indicator organism showed a 2log10 reduction. A manure-only modeled baseline was developed for comparison with the experimental co-digestion data with co-digestion resulting in a 110% increase in biogas production and a tripling of gross receipts with 72% of all receipts being directly due to substrate supplementation. Specific methane productivities for the manure-only and co-digestion scenarios were 0.23 and 0.37m3 CH4/kg VSload, respectively. Addition of substrates tripled project gross revenues and accounted for 72% of all receipts, however, inclusion of substrates led to significant increases in total nitrogen and phosphorous loading to the farm. This is a case specific study limited by the specific substrates and digester technology employed. It is expected that the data and conclusions derived will offer researchers information previously unattainable in regard to data quantity, scale, comparison to manure-only baseline, comparison of commercial-scale performance to laboratory-batch predictions, and application to economics and nutrient balance. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.