Robert Spajić

Using Biochemical Methane Potential Assays to Aid in Co-substrate Selection for Co-digestion

There has been an increasing interest in manure anaerobic digestion; however, economic constraints are still one of the limits to widespread use of the technology in the United States. Co-digestion of manure with other feedstocks has been noted as a way to increase the economic feasibility of animal feeding operation anaerobic digesters via increased energy production potential. A wide variety of materials have been proposed as co-digestion materials, and additional substrates will continue to receive consideration. Biochemical methane potential assays (BMPs) have been reported to provide a first-cut evaluation of potential substrates. This article provides specific details about the BMP assay process used by the Agricultural Waste Management Laboratory (AWML) at Iowa State University (ISU) on agricultural materials and by-products, including the assay method and utilization of the results. Additionally, BMP results from 31 samples assayed in the ISU AWML as broader anaerobic digestion research or as service to the industry have been included. Results showed that the high solid content and non-homogeneity of agricultural materials and by-products can increase variability in assay results. The method utilized here helped limit the effects by utilizing volatile solids concentrations instead of chemical oxygen demand to initiate the BMP assays and to normalize the results. The coefficient of variation for the assays performed in triplicate ranged from1.6% to 33% in which the majority was less than 15%. For five of the substrate types analyzed (beef manure, dairy manure, cheese when lactate permeate, food processing marinate, and enzyme process by-product), multiple samples were assayed from different sources. The sample standard deviations indicated that methane production potential could be affected by material source and that BMP assays reported here should only be used as an estimate when considering which types of materials to assay.

Evaluation of Laboratory Biochemical Methane Potentials as a Predictor of Anaerobic Dairy Manure Digester Biogas and Methane Production

Estimates of the quantity of biogas and methane produced by a dairy manure-based anaerobic digester are an important design parameter; they are used to size collection, transport, and biogas clean-up and utilization equipment prior to digester construction. They are also used to estimate potential return on the producers investment. Current methane production estimation methods include stoichiometric methane production calculations based on manure Chemical Oxygen Demand (COD) content, an estimate of digester COD removal, and data from the past performance of other dairy manure digesters. However, these methods can overestimate the actual biogas and methane production. This paper compares measured anaerobic digester biogas and methane production to estimated production based on laboratory biochemical methane potential (BMP) data developed from manure samples collected at six New York State dairy farms operating anaerobic digesters. Laboratory BMP tests of each digesters influent (manure and food wastes) were compared to on-farm monitored biogas and methane quantities calculated from biogas methane content. These comparisons were used to determine the ability of laboratory BMPs to predict on-farm production from dairy manure digesters. The results suggest that BMP assays could provide useful information to estimate methane production for dairy manure anaerobic systems. The results showed that using BMPs to estimate biogas production may not be accurate, but that predicting methane production with BMPs may be feasible. The linear regression results did not show a relationship that could be used for predicting biogas production from BMPs. However, a relationship and statistical similarities were found for predicting methane production from BMPs.

Croatian Food Industry By-Products: Co-Digestion with Swine Manure vs. Use as Liquid Animal Feed

Food industry by-products such as spent brewers yeast and whey from cheese production are being amended with nutrients and used as a feed source in the Croatian swine sector. However, as interest in energy production and anaerobic digestion of animal manures has increased, co-digestion of these materials with manure could improve the economic viability of on-farm digesters. To determine the feasibility of this approach, consideration should be given to whether food industry by-products provide a better economic return as a low-cost animal feed or as an anaerobic digester feedstock. In addition, while slaughterhouse wastes are not used as an animal feed, this article also considers the use of this material as a co-digestion feedstock. The economic information and substrate selection presented in this article are based on by-products available to a swine farm in Croatia and production data from the facility while feeding with by-products. Biochemical methane potential (BMP) assays were used as a fast, inexpensive method to determine the potential methane production rates for the various substrates. Using BMPs, the potential methane production rates for various combinations of spent brewers yeast, whey, slaughterhouse waste, corn silage, and swine manure were also determined. Results of the BMP assays were used to compare the potential economic return of using the food wastes to produce methane in the digester to the value of these materials as feed ingredients for swine production. Based on live production data, liquid feeding of food industry by-products was calculated to provide a

Soybean Straw, Corn Stover and Sunflower Stalk as Possible Substrates for Biogas Production in Croatia: A Review

6.89 savings per finish pig produced over a 90-day period at the Croatian facility. Since the facility produces 14,000 finish pigs every 90 days, this represents a cost savings of

Development of a Wireless Sensor Network to Quantify Hydrogen Sulfide Concentrations in Swine Housing

96,000 per turn, or over

Anaerobic Digestion of Swine Manures with Different Types of Food Industry Waste

307,000 per year considering that the facility finishes 3.2 turns of pigs per year. Using cheese whey or spent brewers yeast as a co-substrate in the proposed swine manure digester has the potential to provide an additional income via electricity generation of

Anaerobic digestion system selection for Croatian swine manures.

26,000 and

CONVERSION OF ORGANIC MANURE INTO BIOGAS

34,000 over a 90-day period, or

A review of available resources on anaerobic digestion technologies.

83,000 and

Use of Biochemical Methane Potential (BMP) Assays for Predicting and Enhancing Anaerobic Digester Performance

109,000 annually, respectively. These values were based on the value of the substrate, assuming that either a digester or liquid feeding system already existed. Based on the data, the economic return is better when the by-products are used as a feed ingredient. However, if the swine digester is amended with all available co-substrates, including whey, spent brewers yeast, slaughterhouse waste, and corn silage, the potential additional income is