Jay Martin
Ohio State University
Ecological treatment systems are similar to natural wetlands in which the sun is
the primary energy source and microbial interactions in aerobic and anaerobic
environments degrade waste. The difference is that the treatment is controlled
and occurs in tanks in a smaller area. Although ecological systems have been
successful in economically treating municipal wastewater, dairy wash water
presents a challenge due to BOD (biological oxygen demand) and ammonia levels
that are 3-10 times higher. A small-scale system was designed with four
replicated lines to treat 340 gallons of wash water per day from the OSU
Waterman dairy barn. The wash water was collected from the manure holding pond
and added to the system consisting of the following components: 1) anaerobic
digester to break down BOD; 2) anoxic reactor with low levels of dissolved
oxygen for denitrification of ammonia; 3) aerobic reactor with additional oxygen
for nitrification; 4) open aerobic reactor with vegetation to break down BOD,
nitrify ammonia and uptake phosphorus; 5) stratifier for settling of solids; and
6) marsh for denitrification and phosphorus uptake. The wash water circulated
between components 1 through 5 before moving to the marsh and had a total
hydraulic retention of 16.6 days. The system was in operation from June through
October 2004and resulted in significant reduction in ammonia, BOD and coliform
bacteria as well as a reduction in nitrates and phosphorus. However, as the
adsorption of phosphorus to mineral matter is expected to decrease over time, an
additional additive or replacement of mineral matter may be needed. Continued
research on the system will address the challenges of plant die off during
winter, separating solids before adding the wash water to the system,
identifying plants that add value to the system and increasing loading of the
system to allow for larger scale use.
Discussion:
Mike Monnin (NRCS) asked why the process begins in an anaerobic digester. Martin replied that the high carbon concentration (BOD-biological oxygen demand) needs to be reduced at the beginning so that denitrification and re-nitrification is not inhibited.
Lynn Willett (OSU) asked if BOD or COD (chemical oxygen demand) was measured. Martin responded that BOD was monitored as the process is less time consuming; however, he is willing to discuss monitoring COD if there are benefits to doing so.
Fred Michel (OSU) asked how much methane was produced in the anaerobic digester. Martin noted that the amount has not been quantified as yet.
Diane Borger (OSU) questioned the selection process for plant materials in the open aerobic reactor. Martin replied that a good root environment is needed to sustain the microbes that degrade the nutrients. Thus plants that continue to grow root mass even with high nutrient concentrations were used. These plants had been identified in other systems. Additional research is needed to identify plants that could have on-farm uses such as silage.
Maurice Watson (OSU) asked if solids accumulated in the system. Martin noted that the solids that accumulated were about 20% less than found in conventional treatment systems. He speculated that the roots may trap the sediments.
John Smith (OSU) asked how long the plants survive in the system. Martin noted that the amount of nutrients assimilated by the plant is less than 2% of the material in the system as their main role is to provide an ecosystem for the microbes. In the Waterman study, tropical plants were used and did not survive winter temperatures as there was no additional heat added to the greenhouse.
Kip Gardner (OSU) asked if the methane generated in the anaerobic digester could be used for heating. Martin responded that the digester used was low tech and did not provide enough methane for heating. Gardner suggested that a pond system could work.
A Columbus participant asked what total percentage of wash water from the Waterman farm was treated in this system. Answer: about 5%.
Smith suggested that Martin contact Bill Bickert at Michigan State University. Bickert has been working on a new style digester at Green Meadows Farm that moves the liquid through more quickly, increasing the methane produced.
Richard Moore (OSU) asked if an Amish dairy farm with about 30 cows could use the system and noted that some have access to free gas that could be used for heat. Martin responded that the current system could probably be used for 30-40 cows as the four replications would not be needed. As to the gas, the preference is to use the outputs of the system to provide heat.
Watson asked is artificial light is used in the greenhouse. Martin noted that the only light used is if work needs to be done at night; it is not used for growing purposes.
Gardner asked if the effect of the system on viruses had been studied. Martin replied that only coliform bacteria had been analyzed. Future plans are to evaluate the effect on salmonella.
Gardner asked about Ohio impediments to permitting the treatment system. Martin noted that the OEPA would be responsible for regulation. Data indicating that the discharge meets or exceeds water quality standards would be required if there is a discharge. Permitting is not required if there is zero discharge from the system which may be attained by using the treated liquids in a greenhouse or for irrigation.
Tom Noyes (OSU) asked for a clarification of the wash water being treated. Is it from the milking house or the barn? Martin noted that it is from the tie barn and includes the manure as well as sawdust used for bedding. These materials are flushed into the pit during cleaning.
Michel asked how more nitrogen could be used by the vegetation to increase yield. Martin responded that it depends on the vegetation. He currently is not familiar with any that would “hyper-accumulate” nitrogen.
Ted Short (OSU) noted that the air temperature in the greenhouse can affect the vegetation but suggested that the water temperature also be monitored and controlled.
Willett asked if the mass of manure needed to yield the necessary methane to maintain temperatures had been determined. Martin responded that it has not yet been evaluated and noted that the optimal temperature for the greenhouse is 45-50o F.
Michel questioned a diagram showing the loss of ammonia and appearance of nitrate. Why does nitrate not accumulate in the first few tanks? Martin replied that in the first tanks, nitrification is quickly followed by denitrification due to the low oxygen levels in those tanks.
Willet asked about the pH of the system. Martin responded that it is approximately 7 with little variation.
Larry Brown (OSU) questioned how the dairy staff perceived the impact of the system on dairy operations. Martin noted that he thought there was little impact, but had not had feedback from them. The dairy staff was not involved in collecting the wash water from the pit or operating the system in any way.
Brown suggested a demonstration test plot using the wash water for drip irrigation. Martin noted that the wash water collected in the pit is usually disposed/treated via the sanitary sewers.
Martin commented on Ann Christy’s research using manure in a microbial fuel cell to generate electricity. It may be possible to use this electricity to power the blowers used to aerate the tanks and the airlift pumps that move water between tanks, thus decreasing energy inputs from outside sources.
Monnin asked if the treatment system could work for smaller farms that have a more solid manure or for milkhouse wash water which has a high BOD plus some detergents and disinfectants. Martin responded that it could work, especially if settling to decrease the solid content was the first step. Research on municipal treatment systems indicated that ecological systems are fairly resilient; the key is biodiversity of microbes to allow adjustment to system inputs.
Tom Zimmerman (ATI), citing a study he conducted 10 years ago, used wetlands to treat dairy milkhouse wash water. The raw wash water had a BOD of 1500 ppm and included some acids. Martin replied that it is a high BOD and would need to be tested. He will have a class this year that will evaluate the effect of adding acid to the manure treatment system.
Notes by Mary Wicks
The OCAMM (Ohio Composting and Manure Management) Program is funded by OARDC/OSU.