T INEDALE FARM, a fifth genera- tion dairy farm in Wrightstown, Wisconsin, is one of the largest dairy farms in the state with near- ly 2,500 cows. These cows produce approximately 50,000 gallonslday of manure, which are increasingly

becomin~ more difficult to manaqe in an en- vironmentally conscious and cost-effective manner. Several years of research on anaerobic digestion technologies by Carl Theunis of Tinedale Farm resulted in the formation of Ag Environmental Solutions (AES). AES has recently constructed the first temperature phased anaerobic diges- tion (TPAD) system for the dairy industry a t Tinedale Farm.

Farm based anaerobic digestion has typi- cally been accomplished using covered la- goons or plug flow mesophilic digesters. However, one of the stated goals of AES is to maximize the conversion of the manure solids to methane used for power genera- tion. Based on this goal, AES evaluated nu- merous anaerobic digestion technologies be- fore determining that the TPAD system would be most suitable to the dairy. The solids content of the manure a t Tinedale Farm generally ranges from seven to nine percent, which is below what is typically ac- ceptable for plug flow anaerobic digesters, but is acceptable for conlplete mix systems such as the TPAD technology.

The TPAD system was developed and patented by Dr. Richard Dague of Iowa State University in Ames. Since his death, the patent belongs to the Iowa State University Research Foundation. The technology has been installed at some municipal wastewa- ter treatment plants in the United States, in- cluding several in Wisconsin. Results from these facilities, as well as laboratory testing conducted at Iowa State University, indicate tha t the TPAD system achieves higher volatile solids destruction and produces more biogas than other types of anaerobic di- gestion systems. For example, the municipal wastewater treatment plant in Sturgeon Bay, Wisconsin reported an increase in volatile solids destruction on the order of 15 to 20 percent when i t switched from a mesophilic system to the TPAD process. Ad- ditionally, full-scale installations have proven to be capable of producing Class A biosolids (meeting the U.S. EPA's Process To Further Reduce Pathogens [PFRPI require- ments). The same level of pathogen reduc- tion can be achieved with the digested ma- nure. A "Class A" solids would provide farms with the opportunity to develop value-added products such as animal bedding and soil amendments.

The power generated from the Tinedale Farm project is sold as "green power" to Wis- consin Electric Power Company (WEPCO). Wisconsin is one of several states that cur- rently has Renewable Portfolio Standards requiring utilities to generate a specific per- centage of their total production from re- newable energy sources such as biomass. Therefore, utilities are actively seeking out,

Anaerobic Digestion Advances

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TOTAL TREATMENT PACKAGE

TEMPERATURE PHASED ANAEROBIC

DIGESTION OF DAIRY MANURE

Wisconsin farm installs a t w o phase thermophiliclrnesophilic digester and is pilot

testing solids separation and wate i clarification technologies that wil l result in a more closed loop manure management system.

John E Katers

and in some cases providing significant fi- nancing for renewable energy projects such as the one at Tinedale Farm.

SYSTEM DESIGN Manure from the free-stall barns a t

M~~~~~ from the ~ i ~ ~ d ~ l ~ F~,., , , Tinedale Farm is collected continuously us- dairy barns feeds the anaerobic ing a dry scraping system. The manure then digester located beneath the flows by gravity froin the barns to a contin- gravel covered berm. ually mixed equalization basin that is locat-

clarification processes. The biogas from the digester is sent

to the biogas handling system, which in- cludes equipment to remove moisture and hydrogen sulfide, which can com- bine to form sulfuric acid that can sig- nificantly damage and shorten the effec- tive-Kfetz%hegene~abreThe-cleaned biogas is then sent to the two 375 kW generators where it is converted to elec- tricity and sent to the power grid. A flare also is in place to handle any excess bio-

The TAPD system gas from the TPAD system. incorporates several key components including: INITIAL RESULTS 1 ) heat exchangers used The TPAD system at Tinedale Farm began to raise the manure operating in the late spring of 2001 as a to thermophilic mesophilic system. Only recently has the first temperatures, 2) an H2S filter for the digester gas, phase of the TPAD system been converted to 3) hot water recovery starting at thermophilic temperatures. from the generators and The sawdust bedding has been problem- 4) a pilot water atic for the digester system because of diffi- treatment system for the culties with pumping. It is hoped that even- digester liquid effluent. tual use of the Class A digested solids for

bedding will eliminate this problem. During the initial period of operation, a

considerable amount of time has been spent evaluating the reliability of equipment to ensure that the TPAD system can handle the continuous operations needed for the initial project as well as those constructed at other farms in the future. Attention also was

1- ed adjacent t o the anaerobic digestion sys- focused on minimizing the maintenance re- tem. The equalization basin acts as a stor- quirements of the various system compo-

This project age tank that provides a continuous feed to nents, as this is a critical concern for farm- the digester. ers interested in anaerobic digestion. Even

represents an The manure is pumped from the equal- though a thorough economic analysis of the ization basin through a heat exchanger to project hasn't been completed because

0pport~nity to achieve thermophilic temperatures (120" to steady-state operations under TPAD oper- 135°F) prior to entering the thermophilic ating conditions have not yet been achieved,

obtain phase of the TPAD system. (The digestion AES estimates that this project will have a

environmental process doesn't create enough heat on its payback period of approximately five to sev- own.) The heat exchanger utilizes recovered en years. heat from the water jackets of the two 375 One side benefit noted during the initial benefits kW engine generators that operate on the operation is that the monitoring and labora-

providing an biogas produced by the TPAD system. The tory testing of the TPAD system has allowed water jackets cool the generators, which Tinedale Farm to identify other operational

additional profit produce substantial heat while burning the issues such as water use. In several cases, biogas. In the tube-in-tube heat exchanger, small but noticeable changes in the flow rate

center for the dairy a pipe carrying the manure runs inside a to the TPAD system have alerted Tinedale

industry. pipe with the hot water, thereby transfer- Farm to the fact that a hose was left running ring the waste heat from the generators to elsewhere in the facility or there was a leak- the incoming manure. ing valve that needed to be fixed. Although

The thermophilic reactor is completely this seems to be a minor benefit, the costs mixed using two draft tube style mixers. associated with hauling this additional wa- The partially digested manure is then ter off-site for land application can be sig- pumped from the thermophilic reactor nificant. In effect, the monitoring of the through a cooling heat exchanger, which TPAD system has provided a good indicator brings the temperature down to mesophilic of the overall farm operations. Taking this a temperatures (85" to 100°F), and into the step further, as increased nutrient testing of mesophilic reactor. The mesophilic reactor, the TPAD system is initiated, it is also pos- which consists of two equally sized com- sible that cattle feed ratios also can be mod- partments, is completely mixed using four ified based on the testing of the TPAD sys- draft tube style mixers. The digested ma- tem influent. nure then flows out of the ~ ~ A ~ - s ~ s t e m by gravity to the existing lagoons for storage ADDITIONAL PROJECT PHASES - and lakd application. Yheuretention timeif According to Carl Theunis, the digester is the entire TPAD system is approximately just one component in the whole system to 15 days. Tinedale Farm also is evaluating process the manure in a way that is eco- further treatment systems for the TPAD ef- nomical for dairies. AES is focusing on pe- fluent, including solids handling and water ripherals, including solids separation; treat-

ment of the liquid (including effluent clarifi- cation with the goal of getting the water clean enough to give back to cows to drink); and conversion of the solids into value- added products, including bedding for the cows. The majority of the ongoing research and development is being completed a t

- --TinedaleFGirm. -- - . -. -

Preliminary testing has determined that traditional agricultural separators such as rotary screens have some difficulty with the smaller solids associated with digested manure, resulting in an effluent from the separator that still contains a substantial amount of,solids. Capturing a higher per- centage of these solids is critical in terms of the amount of digested solids that will be available for reuse a s well as the impact on water clarification. Failure to capture these solids in the separator will ultimate- ly reduce the amount of solids available for value-added products and make water clarification more difficult and costly. (Municipal wastewater treatment plants with TPAD systems use belt filter presses for dewatering.) More testing with agricul- tural separators will take place, as will ad- ditional research on the fate of the nutri- ents in both the solids and the liquids from the separators.

The dewatering and drying of the digest- ed manure for use as animal bedding, soil amendments or for composting with other materials such as yard trimmings and in- dustrial food residuals hold meat promise.

grant of $44,400 to the University of Wis- consin-Green Bay that has allowed gradu- ate students from the Environmental Sci- ence and Policy program the opportunity to inonitor and evaluate the overall TPAD sys- tem performance. The project's potential im- pact on Wisconsin's economy was among the

-.s~i.t~~ia-t~at-led-the-.~.n.i-v-e~si.ty-to-fu.ndddthe.~- grant, according to Albert Beaver, interim senior vice president for academic affairs a t the University of Wisconsin. It is anticipat- ed that several additional research opportu- nities will emerge as. solids management and effluent clarification components of the project continue to move forward. The pro- ject also has received considerable support from several other state agencies in Wiscon- sin as the level of interest in this area is ex- tremely high.

Although the TPAD project at Tinedale Farm is in the preliminary stages, it ap- pears to hold great promise for the agricul- tural industry. This will be particularly true as the additional project phases for solids separation and water clarification are ad- vanced. This project represents an opportu- nity to obtain environmental benefits while also providing an additional profit center for the dairy industry. W

John Katers is assistant professor, Natural and Applied Sciences, Ciuil l Enuironmental Engineering, at the University of VC7isconsin in Green Bay.

Dewatering digested manure for use as animal

bedding, soil- amendments or for composting with other feedstocks hold great promise.

also-being tested a t Tinedale F'aim, with preliminary results being extremely posi- tive. Water clarification is a very important BAT 506 HTR and HTI component of the ~ \ ~ e r a l l project, as this would substantially reduce the hauling costs associated with the land application of liquid manure! a s well as reduce water needs for the farm, which can be a critical is- sue in geographic areas with limited water availability. Hauling costs to land apply ma- nure can typically be in the range of one to two cents/gallon - a substantial annual op- erating cost for large o~e ra t ions such as - A

~ineda je Farms. I 1 A PARTNERSHIP APPROACH

The Tinedale Farm project represents an innovative partnership between the public and private sector. STS Consultants, Ltd. was the local engineering firm utilized for the project design and start-up. In addition, a faculty member from the University of Wisconsin-Green Bay was actively involved in the design of the TPAD system. The Uni- '

versity of Wisconsin System awarded a

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