EXECUTIVE SUMMARY

SLP LINK Project LK0650

Dairy farm dirty water: seeking the best solutions to avoid pollution

(DW-STOP)

Start date: 01/08/2002End date: 31/07/2005

Partners:ADAS Consulting Ltd

Agricultural Requisites and Mechanisations Ltd

Carrier Pollution Control Ltd

Cranfield University

Institute of Grassland and Environmental Research

Milk Development Council

National Soil Resources Institute

Pallinghurst Farm Partners

Silsoe Research Institute

University of Birmingham

Sponsors:Department for Environment, Food and Rural Affairs (Defra)

BOC Foundation for the Environment

Figure 1. Dirty water is a serious problem on many UK dairy farms

Most UK dairy farms produce large volumes of liquid wastes from dairy parlours and collecting yards. Usually, irrigation to land is the best way to manage this “dirty water” (DW), but the associated pollution risk is considerable, e.g., the total pollution load from 200 dairy cows is equivalent to the sewage from 3600 people and about 25% of this is in the DW. Hence, the objectives of this work were to identify, develop and assess the best practical means at minimal cost to reduce the risks of water pollution and pathogen transfer caused by DW irrigation to land, and to illustrate this by specifying two full-scale treatment systems.

Four pilot-scale treatment strategies: down-flow reed beds (DRB), percolating soil plots (PSP) , overland flow plots (OFP) and settlement plus intensive aeration (IAP) were each developed to treat 500 l/day, and all were evaluated on a 440-cow commercial dairy farm. A comprehensive set of performance indicators was used during two trial periods of 50 and 46 weeks respectively. The impacts of land spreading both untreated and treated DW were assessed using three in-field lysimeters, whilst complementary laboratory-scale studies provided further data for subsequent mathematical modelling of the treatment and land-spreading processes.

The farm site provided a rigorous test, with 5-day Biochemical Oxygen Demand (BOD5) and Total Solids (TS) values ranging from 600 to 12000 mg/l and from 300 to 18000 mg/l respectively, with substantial seasonal variations, thus resembling the range of DW characteristics previously observed on other UK dairy farms. During Trial 1, all four systems treated this effluent effectively with average reductions of over 80% in BOD5 and 40% in TS. Comparable results were found with: chemical oxygen demand (COD), total and ammoniacal nitrogen, nitrates, nitrites, phosphorus (P) and thermotolerant coliforms. The results defined the boundaries of efficient and reliable operation so that changes implemented in Trial 2 improved performance in several ways. Trial 2 provided the data required for development and validation of mathematical models to specify full-scale OFP, IAP and DRB treatment systems, and to compare their costs and effectiveness. The lysimeter and laboratory-scale data facilitated a DW-SOIL model, to help avoid the inefficiencies of treating DW beyond environmental needs and to prevent P accumulation and leaching in soils that receive DW.

Through the models, the project reached its goal of providing the means to define sufficient but not excessive DW treatment prior to land spreading. This was illustrated using two full-scale case studies based on real farm data. The models could also meet other commercial requirements, e.g. treatment of dairy farm DW before certain forms of re-use; discharge/re-use of vegetable wash water and leachate from landfill sites; and alternative means of sewage treatment for isolated rural communities. The project has also provided a data set that uniquely defines the properties of DW and their seasonal variations on a large commercial dairy farm in the UK. Further studies using this data could reveal more about the impacts of herd management and weather factors on DW production, with implications for the design and management of DW systems.

The observations and occasional problems encountered during completion of DW-STOP have indicated why certain assumptions and practices concerning the production and management of DW should be re-assessed in the interests of safe and efficient dairy production, and of practical environmental protection. For example, this includes possible interactions between certain soils and sodium in DW, resulting from the use of dairy cleaning chemicals.

Effective exploitation of the results from DW-STOP by UK dairy farmers requires a well-planned communications strategy including a full-scale demonstration project to highlight the benefits and reduced costs, also to show milk retailers and consumers that milk production can benefit the environment through efficient recycling. This would complement further dissemination through the publication of a generic booklet on DW Management, compatible with Defra’s current “Managing Livestock Manures” series. The project impinged on Defra’s “Agricultural Waste Regulations Consultation” in March 2005, by identifying DW treatment technologies as part of a farm manure management strategy to protect the environment. It would be unfortunate if significant regulatory barriers prevented or seriously undermined future DW treatment developments.

Figure 2. The four dirty water treatment systems included in the DW-STOP research project: settlement and intensive aeration (top left); down-flow reed beds (top right); percolating soil plot (bottom left) and overland flow soil plot (bottom right).

CONTACT
Dr Trevor Cumby



1