Design, Construction and Implementation of a Pilot Scale Anaerobic Digester at the University of Missouri-Columbia’s Swine Teaching and Research Farm

Animal Manure Management November 06, 2013|Print

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Abstract

Animal manure is often utilized by the American agriculture industry as fertilizer without considering the potential energy production. It is well established that on-farm anaerobic digestion (AD) can be effective in providing energy, reducing greenhouse gas emissions, and controlling air and water pollutions. Knowledge of the ADs on biogas production, digested and stored manure nutrients, and air emissions must reach parties of interest. A modular, pilot-scale, mesophilic AD system is being installed for the new swine finishing facility at University of Missouri-Columbia Research Farm.

The new AD design utilizes three insulated, reinforced fiber-glass tanks of 2500-gallon in size, which are commercially available. One tank is designed for feedstock storage and mixing, and the other two tanks are for digestion. The dual-tank set up provides research flexibility as either single stage with two-stream parallel replication or dual-stage single-stream experiments. The design employs small biogas (generated by the AD) boilers for heating the digester tanks and system building.  It also features a feedstock-digestate heat-exchanger for heat reclamation to reduce net energy input; which will be critical to the small and mid-size AD systems not generating electricity (no waste-heat from engines).

Self-scraping system in hog confinement building.

The system also includes a geothermal heat exchanger for biogas cooling to collect condensate in the biogas along with a small iron sponge to reduce H2S concentrations which improves the biogas quality. Excess biogas will be burned in boiler and the heat produced will be dissipated through a dual purpose radiator. The radiator provides building heat in winter and releases heat outside in summer. The goals of this project are to demonstrate AD for small and mid-size swine productions, quantify and characterize manure nutrient changes due to AD and storage, and develop baseline emission factors for raw and digested manure. This paper reports the design, construction and implementation of the AD system.

Why Study Small-Scale Anaerobic Digestion?

The purpose of this project is to establish a pilot scale, on-farm anaerobic digester (AD) that demonstrates and evaluates the potential energy production, manure management, and overall economic viability of such systems. This research will provide invaluable information for small to medium sized swine farms seeking viable energy alternatives, practical manure management practices and air quality improvements.

Valve control box (under construction). This allows extra manure and effluent to be discharged directly to the lagoon or to pump fresh manure directed back to the digester.

What Did We Do?

Construction began in the Fall of 2012, at the University of Missouri-Columbia’s Swine Teaching and Research Farm. This modular, pilot-scale, mesophilic AD system is being constructed next to a four-room swine finishing research barn. Each of the finishing room has individual deep-pit storage, with a  pull-plug system for draining the manure to the lagoon. Manure scraper systems are installed in two of the rooms to more frequently collect the manure. The AD system is comprised of three insulated, reinforced fiber-glass tanks, each with a capacity of 2500-gallons. The first tank is designed for feedstock storage and pre-mixing, while the other two are for digestion. The dual tank set up allows flexibility for researchers to conduct experiments either with a single stage, two-stream parallel replication or dual-stage single-stream digestion process. The system employs a biogas (generated by AD) boiler for heating the digestion tanks to maintain continuity. A 3,000 gallon biogas bladder storage unit stores the biogas for a few hours. A feedstock-digestate heat exchanger is designed for heat reclamation to increase net energy output; which will be critical to a small to mid-size AD systems that do not generate electricity (no waste-heat from biogas engines). The boilers also supply heat to the AD housing through radiators, while the excess biogas will be flared off.

Current digester system enclosed in greenhouse.

What Have We Learned?

Designing and implementing an AD system is complex and time consuming. It is very important to involve a good engineering or technical support team. If the barn is not designed to accommodate an AD system, significant consideration is needed to manage the manure collection and transport, and to maintain manure freshness and solids content. Project management is critical to consider planning and coorperation between the farm personnel and management, utility and construction companies, and the engineering support firm.

Future Plans

Pilot test will be conducted to examine and fine-tune the system. The AD system is designed for research and demonstration purposes. Submitted proposals include plans for studying the improved efficiency due to better design and heat-exchangers, effects of feedstock, co-digestion, feedstock pre-treatment on biogas production, and characterizing greenhouse gas emissions from untreated manure and AD-treated manure.

Authors

Brandon Harvey, Research Assistant, Agricultural Systems Management, University of Missouri bchfzf@mail.missouri.edu

Teng Lim, Assistant Professor, Agriculture Systems Management, University of Missouri. Kevin Rohrer, Engineer, Martin Machinery, LLC.

 

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