Managing Dairy Waste Using Constructed Wetlands - Composting

Managing Dairy Waste Using Constructed Wetlands - Composting

Summary

Summary
This project is exploring two alternative technologies — constructed wetlands and composting — to treat and manage liquid (milking parlor effluent) and solid (barn manure) dairy wastes. The research addresses the environmental and economic viability of these technologies, which may be best management practices for treating livestock waste.

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

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

* To train certified nutrient managers and extension personnel throughout Maryland in the use of constructed wetlands and composting.

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

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

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

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

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

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

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

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

* To evaluate the possible profit from marketing composted materials.

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

Findings to Date
The initial water quality analyses indicated that the wetland system is providing a high level of treatment. However, the pretreatment structures (a settling basin and an aerated tank) were resulting in relatively little removal of most constituents.

Wetlands are probably unsuitable for treating highly concentrated dairy waste, but are effective in sustainably removing nitrogen and phosphorus from waste waters that have been pretreated to remove the bulk of suspended solids and reduce elevated ammonia concentrations.

Economic analyses indicate these systems may be useful as components of integrated waste management systems for dairy facilities.

Methods and Findings
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 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.

The majority of our objectives have been met. We completed the composting study in 1996 and the economic analysis of composting and constructed wetlands in 1997. We finished construction of the wetland treatment system (including settling basin and aeration tank pretreatment structures) in 1997. This 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 of 1997, and we have collected samples monthly from various points throughout the system, Our analysis covered biochemical oxygen (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), ammonia, nitrate/nitrite, total nitrogen, ortho-phosphate, total phosphorus, dissolved oxygen, temperature, pH, and electrical conductivity.

The initial results of water quality analyses indicated that the wetland system provides a high level of treatment, with removal efficiencies above 90% for most parameters. However, our data also indicated 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.

During 1998, we continued our monthly water quality monitoring and description of changes in wetland plant community structure. Early in the 1998 growing season we observed browning of wetland vegetation near the waste inflow point, possibly the result of elevated ammonia concentrations. We collected plant samples for biomass analysis at inflow and outflow points to assess the reduction in growth due to stress.

Because of the low efficiency of the pretreatment structures and the potential for stress to vegetation, we modified the system to obtain waste from two large settling ponds. Although the ponds receive waste from the entire dairy operation, its outlflow had lower waste concentration. This is wastewater that would otherwise be recirculated through the system or applied to fields.

In 1997 we held a well-attended in-service training workshop for livestock and nutrient management specialists on constructed wetlands and composting.

Our findings to date indicate that wetlands are probably unsuitable for treating highly concentrated dairy waste, but are effective in sustainably removing nitrogen and phosphorus from waste waters 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

Reported January 1999. 1999 Northeast Region SARE/ACE Report.

Collaborators: