Managing Dairy Waste Using Constructed Wetlands - Composting

Final Report for LNE95-062

Project Type: Research and Education
Funds awarded in 1995: $110,305.00
Projected End Date: 12/31/1999
Matching Non-Federal Funds: $129,250.00
Region: Northeast
State: Maryland
Project Leader:
Leslie Cooperband
University of Maryland
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Project Information


Disposal of dairy waste has become an important issue for moderate to large-scale confined-animal dairy farms. In many instances, more manure and liquid waste are produced than can be applied safely to surrounding crop fields, particularly in areas where herd sizes per unit area of land are increasing. Current modes of waste treatment and disposal include direct land application of solids and temporary storage of liquid wastes in lagoons followed by land application. These practices can lead to nutrient saturation of soils and release of nutrients and solids to streams, lakes, and estuaries. In this project we are exploring the use of two alternative technologies, constructed wetlands and composting, to treat and manage liquid (milking parlor effluent) and solid (barn manure) dairy wastes. Our research addresses the environmental and economic viability of these technologies, which may be best management practices for treating livestock waste.

We have met all of our objectives. We completed the composting study (Objective 3) in 1996 and in 1997 year completed the economic analysis of composting and constructed wetlands (Objective 4). Additionally, we completed construction of the wetland treatment system in 1997 (including settling basin and aeration tank pretreatment structures), which had been delayed due to unusually wet weather during 1996 and by dieback of some of the planted vegetation over the winter of 1996-97. The first milking parlor effluent was introduced into the wetland cells in September 1997, and we collected samples for water quality analysis in between October 1997 and December 1998 of inflowing and outflowing water from the settling basin, aerated tank and cells to assess treatment efficacy (Objective 2). Analytes included biochemical oxygen (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), ammonia, nitrate/nitrite, total Kjeldahl nitrogen (TKN), ortho-phosphate, total phosphorus, dissolved oxygen, temperature, pH, and electrical conductivity. Finally, in June 1997 we held a well-attended In-Service Training Workshop for livestock and nutrient management specialists on constructed wetlands and composting (Objective 1). At this workshop we presented the results of our composting research, described the construction of the constructed wetland system, and presented the findings of the economic analysis of these alternative waste management practices for dairy farms.

The results of water quality analyses indicate that the wetland system is providing a high level of treatment. Overall removal efficiencies were 75% or higher for ammonia, TSS, total phosphorus, and in the range of 50-75% for ortho-phosphate and TKN. Our data also indicate that the pretreatment structures (a settling basin and an aerated tank) were resulting in relatively little removal of most constituents, with the bulk of the removal occurring in the wetland cells themselves. Because of the low efficiency of the pretreatment structures, and the potential for stress to vegetation (we observed some dieback of vegetation near the wastewater inflow), we modified the system in June 1998 to receive waste from two large settling ponds receiving waste from the entire dairy operation, but which we expected to have lower waste concentration. This is wastewater that would otherwise be recirculated through the system or applied to fields.

Economic analyses of the wetland and composting systems indicate that construction and operational costs are similar or less than those of conventional waste management practices. The actual costs will vary depending on the system configuration adopted and the equipment and materials available to the farmer (our cost estimates assume construction work will be done entirely by outside contractors).

Our findings indicate that wetlands are probably unsuitable for treating highly concentrated dairy waste, but are effective in sustainably removing nitrogen and phosphorus from wastewaters that have been pretreated to remove the bulk of suspended solids (which will eventually fill in the wetland cells) and reduce elevated ammonia concentrations (which can kill wetland vegetation). Because our economic analyses of the wetland and composting systems indicate that construction and operational costs are similar or less than those of conventional waste management practices, these systems may be useful as components of integrated waste management systems for dairy facilities.

Project Objectives:

1. To educate farmers and others about low-cost options for the management of dairy waste.

a) To promote more sustainable options for dairy waste disposal for farmers and provide opportunities for supplemental income generation.

b) To train statewide (MD) certified nutrient managers and extension personnel in the use of constructed wetlands and composting.

c) To expose both rural and surrounding urban communities to alternative, environmental-friendly waste management systems.

2. To determine the effectiveness of constructed wetlands in treating dairy parlor effluent.

a) To evaluate the use of waste pretreatment structures in improving the efficacy of constructed wetlands.

b) To assess effects of seasonality on the wetlands’ ability to treat waste.

3. To demonstrate the feasibility of using composting to deal with solid dairy waste.

a) To test several low-tech composting methods for stabilizing solid waste from dairy barns and parlor.

b) To evaluate potential feedstocks for co-composting of dairy waste.

4. To assess the economic feasibility of establishing alternative waste management practices on dairy farms.

a) To evaluate the possible profit from marketing composted materials.

b) To compare costs of conventional dairy waste treatment systems with those of constructed wetlands and composting.


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  • Andrew Baldwin


Materials and methods:

The composting and constructed wetland systems are located at the Clarksville Facility, Central Maryland Research and Education Center, Ellicott City, Howard Co., Maryland (CMREC). The facility includes a dairy farm and is part of the University of Maryland Agricultural Experiment Station network of research farms. The farm is located in a region experiencing a rapid transition from agricultural to suburban land use and is situated roughly midway between the Washington, D.C. and Baltimore metropolitan areas. The site is also a mere 150 meters from the Middle Patuxent River, one of the top priority rivers in the State of Maryland with regard to nutrient pollution of the Chesapeake Bay. The dairy farm includes 100 cows, with 80 cows in milk production. The facility also includes several hundred acres in cropland including cash grain, pastures, and alfalfa.

Research results and discussion:

Education (Objective 1): On June 20, 1997 we held an In-Service Training Workshop at the Central Maryland Research and Education Center (CMREC), Clarksville Facility (Ellicott City, MD) entitled "Constructed Wetlands and Composting for Sustainable Livestock Waste Management." The five-hour workshop was attended by about 35 livestock and nutrient management specialists, including extension agents, nutrient management consultants, educators, graduate students, and university professors. Topics included presentations on design and construction of the constructed wetland system, the research results from the composting study, and the results of the economic analysis. We also led a tour of the constructed wetland system and conducted a demonstration of windrow composting technology. The workshop was also an opportunity for participants to become familiar with the CMREC and included a discussion of extension uses of the facility with the facility director. Finally, the wetland system was featured at a field day held at the CMREC in June 1998 that was attended by several hundred people.

Constructed Wetlands System (Objective 2): The wetland cells were constructed and planted with vegetation 1996. Based on vegetation monitoring, some of the plantings died during the winter of 1996-97, so we replanted portions of the cells in June of 1997 and allowed this vegetation to grow before introducing waste into the cells. Construction of the pretreatment structures (a settling basin and an aerated tank) was completed during the summer of 1997, and waste was introduced into the cells in September. The design of the constructed wetlands system (Fig. 1, Attachment A) allowed us to test the effectiveness of two levels of pretreatment (a passive system involving only the settling basin and a mechanical system involving the aerated tank in addition to the settling basin).

To assess baseline conditions we collected soil and surface water samples before introducing waste into the cells. After introducing waste, we collected surface water samples from the cells and the pretreatment structures in October and November. Our data indicate that the wetland system is providing a high level of treatment (Table 1, Attachment A). Overall removal efficiencies were 75% or higher for ammonia, TSS, total phosphorus, and in the range of 50-75% for ortho-phosphate and TKN. Changes in concentration were statistically significant for all parameters (two-tailed t-test, P < 0.05). Our data also indicate that the pretreatment structures (a settling basin and an aerated tank) were resulting in relatively little removal of most constituents, with the bulk of the removal occurring in the wetland cells themselves (Table 1, Attachment A). Changes in concentration were not significant for all parameters except for TKN, which increased in the Settling Basin (P = 0.0438). Because of the low efficiency of the pretreatment structures, and the potential for stress to vegetation (we observed some dieback of vegetation near the wastewater inflow), we modified the system in June 1998 to receive effluent from two large lagoons receiving waste from the entire dairy operation. The barnyard and milking parlor effluent from the farm flows through a solids separator, and then through the lagoons to remove additional suspended solids and break down oxygen-demanding substances. The wastewater is then normally recirculated through the system as washwater or applied to fields. Our objective in modifying the wetland system was to reduce the influent concentrations of ammonia and solids to the wetland cells. This role of wetlands is comparable to that of wetlands that have been used in treating domestic sewage, i.e., as a tertiary treatment unit for removal of nutrients. The wetland cells maintained a relatively uniform effluent concentration of most parameters despite fluctuations in the quality of influent wastewater (Figures 2-8, Attachment A). Before modification of the system in June 1998, there were dramatic fluctuations in quality of influent water. Influent levels of TSS and COD were lower after the wetland cells began receiving lagoon water. With the exception of a spike in March and April 1998, levels of other parameters remained similar or, in the case of ortho-phosphate, actually increased. These data suggest that the lagoons are functioning to remove organic oxygen-demanding dissolved and particulate matter (a primary and secondary level of treatment) but doing little to remove nutrients (tertiary treatment). The wetland cells are functioning as a tertiary treatment unit. There was a significant linear relationship between BOD and COD concentration (Fig. 9, Attachment A). This relationship is useful in predicting BOD from COD. Composting (Objective 3): In June 1995, we established four piles (combinations of barn manure, municipal solid waste (MSW) compost, and wheat straw) using the Passive Aeration Windrow System (PAWS). The PAWS method is a passive approach to composting which requires premixing compost feedstocks and placing the mixture atop perforated PVC pipes. The ends of the pipes are uncovered so that as air passes through them it is warmed by the compost and moves convectively up through the pile. This method requires no turning, hence no need for windrow turning equipment. The four piles were: 1)1:1 MSW:pit stored manure (A); 2) 1:0.5:2 MSW:straw: pit manure (B); 3) 2:1:2 MSW:straw:raw manure (C) and 4) 3:1:2 MSW:straw:bedded manure (D). Materials were mixed with a feed mixing wagon and a front-end loader. We monitored O2 and temperature at three depths in each pile weekly for approximately six months. Pile A (1:1 MSW:manure) produced consistently higher temperatures and consumed more oxygen than the other three piles which contained varying amounts of straw. Carbon to nitrogen ratios, a measure of compost maturity, were reduced to 20:1 after 3+ months in the two piles with little to no straw. These findings suggested more efficient, aerobic composting in piles with mostly MSW; given that the straw had not been chopped finely prior to use, the piles with significant amounts of straw were probably too porous to maintain high temperatures. In 1996, we constructed eight compost piles using the PAWS method. The feedstock combinations included: barn manure + municipal leaves + wheat straw (2:1:0.25); manure + wheat straw (5:1); manure + shredded newspaper (6:1) and manure + switchgrass (5:1). Combinations were based on achieving optimal initial C:N ratios (25-35:1) and moisture contents (45-60%). Each feedstock combination was evaluated in duplicate. Feedstocks were chopped finely, mixed with a feed mixer and placed on PVC pipes as described previously. We monitored compost pile temperature, oxygen status, moisture content and microbial activity among other parameters for five months. Results showed that piles with either shredded newspaper or switchgrass (a warm season grass under consideration for riparian buffer use) attained the highest temperatures and oxygen consumption. All of the piles did reach the high temperatures considered critical for killing pathogens and weed seeds. Despite the effectiveness of PAWS for composting certain types of waste, it may not be practical for some farmers from a labor standpoint. We found that PAWS requires that feedstocks be well-mixed before they are set on PVC pipes, a process that involves substantial time on a daily (or at least several times a week) basis. Conventional windrow turning requires more investment in equipment but less constant attention to operate, a factor which may make it more attractive to farmers. Economic Analysis (Objective 4): The economic analysis indicated that costs of building and operating the wetland and composting systems are similar or less than those associated with conventional waste management technologies. It is important to keep in mind that actual costs will vary depending on the capacity of farmers to build and operate the systems without outside contractors. For example, if the farmer has access to earthmoving equipment, construction of wetland treatment cells would be greatly reduced. Another consideration is cost-sharing; wetland systems are not currently eligible for cost-sharing, and composting is eligible for cost-sharing on a case-by-case basis. Cost-sharing would help these alternative technologies to become cost-competitive relative to conventional technologies. And finally, our estimates do not include costs for land for spreading; this may be particularly important in areas such as suburban and rural Maryland where development is increasing pressure on farmers to have larger herds on smaller plots of land.

Participation Summary


Educational approach:

The results of our research were used as a demonstration project for the Annual Better Composting School, a three-day workshop for composters throughout the country (this school is hosted by the University of Maryland and is nationally recognized). Participants in the workshop visited the Clarksville site in October 1996 and used samples from the compost piles in various exercises. The compost monitoring work was performed by a teacher intern who planned to incorporate what she learned into her 7th grade science class. She was part of the Lockheed-Martin Fellowship Program, a public-private partnership that sponsors science teachers to work with scientists over the summer and incorporate lessons learned into their classroom activities. Additionally, two graduate students from the University of Maryland have conducted their M.S. research on the constructed wetland treatment system.

We presented our findings at the In-Service Training Workshop described in section 3A. Additionally, we gave tours of the composting and wetland systems for the Dean of the College of Agriculture and Natural Resources and the Provost of the University of Maryland during 1997. We gave a presentation on and tours of the wetland system at a field day at the CMREC in June 1998, which was attended by several hundred people. Finally, we presented our findings at the Society of Wetland Scientists Annual Meeting in June 1998 and will be presenting additional data on the project at the Northeast Agricultural and Biological Engineering Conference in August 1999.

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Project Outcomes

Impacts of Results/Outcomes

Effects on Production, Environment, and Profits

This project has the potential to offer livestock farmers alternative strategies for livestock waste management. While initial capital costs and labor required for building a wetland treatments system may be similar to those associated with current means of animal waste treatment, the wetlands should become a relatively self-sustaining system once the plants are well established. This may be particularly important in regions such as Maryland where years of land application of wastes has led to saturation of soils with nitrogen and phosphorus. Nutrient saturation of agricultural soils is thought to be a primary contributor to outbreaks of toxic algae such as Pfiesteria piscicida and nuisance algae blooms in receiving waters. Phosphorus is usually the limiting nutrient for algae in fresh water, and our results suggest that conventional treatment technology (the lagoons) are not effective in removing phosphorus, while wetland systems are. Additionally, factors such as reduced availability of land for waste disposal may increase the attractiveness of constructed wetlands and composting for waste management.

This project has also quantified the effectiveness of two levels of waste pretreatment in conjunction with constructed wetland technology. Effectiveness data are critical for determining the level of pretreatment (passive or mechanical) necessary for constructed wetlands. Based on our water quality data, more widespread implementation of wetland treatment systems for agricultural operations will improve water quality in downstream streams, rivers, lakes, and estuaries as long as they are used in conjunction with pretreatment systems (e.g. lagoons) to reduce solids input.

The project also demonstrates the economic feasibility of solid waste treatment through composting. Our research indicates that mature dairy manure compost can be produced using a variety of either on-farm or urban carbon sources and a low-technology approach (the PAWS method). However, implementation of PAWS requires attention daily (or at least several times a week), which may make it less attractive to some farmers than conventional windrow composting.

Economic Analysis

The results of our economic analysis (Objective 4) are presented above under section 3A. Basically, our results indicate that constructed wetlands are similar or lower in cost than conventional technologies, and may offer advantages under some circumstances (e.g., if land is limited or soils are saturated with nutrients). The alternative PAWS composting method is effective but may not be readily adopted by farmers due to a need for relatively continuous attention.

Farmer Adoption

Changes in Practice

Extension staff and nutrient managers and specialists comprised a majority of the participants at the In-Service Training Workshop we held at the CMREC this summer. Overall, their response to composting and constructed wetlands as alternative waste management strategies was favorable, which should result in more adoption of these technologies by farmers.

Operational Recommendations

Our results suggest that farmers should pursue conventional composting techniques using a tractor-pulled windrow turner if they can afford to buy one. The PAWS system will involve fewer initial investment and operational costs and therefore may be more appealing to small farmers. Constructed wetlands should be built to treat effluent from conventional treatment technologies such as lagoons that may reduce solids content but do little in terms of nutrient removal. Recent increases in regulation of nutrient releases such as Maryland’s Water Quality Improvement Act are likely to force farmers to greatly reduce application of manure and wastewater to fields, making implementation of tertiary treatment systems such as wetlands a necessity.

Producer Involvement

At the In-Service Training Workshop we had discussions with extension staff, nutrient managers, and others at the workshop about what they needed in terms of research at agricultural experimental facilities. About 35 people attended the workshop. Previously we had approximately 60 participants in a demonstration of the composting project through the University of Maryland’s Annual Better Composting School. The field day held at the CMREC in June 1998 was attended by several hundred people.

Areas needing additional study

The role of wetland vegetation in treatment effectiveness and the suitability of various plant species for use in constructed wetlands have not been well-studied. Due to stressors in dairy waste such as ammonia (which is toxic to plants at elevated concentrations) and low dissolved oxygen levels (which results in oxygen stress), wetland vegetation may die back or shift in composition. Knowledge of which species are most suitable for dairy waste treatment wetlands would reduce planting costs for farmers and increase survival of planted vegetation. On-site vegetation monitoring should therefore be conducted in conjunction with water and soil sampling to identify levels of waste constituents that cause dieback or community changes in vegetation.

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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.