The composition of dirty water on dairy farms in Ireland.

Considerable quantities of dirty water, composed of milking parlour wash-water, milk
spillages, runoff from cattle yard areas and, possibly, effluent from silage and manure,
are produced on dairy farms. In Ireland, dirty water from dairy farm facilities is normally
managed by spreading on, or irrigation to, land. It has considerable potential
to cause water pollution due to its high pH, 5-day biochemical oxygen demand and its
N and P concentrations. The objective of the present study was to contribute to better
management of dirty water on dairy farms by providing estimates of its composition
using rapid methods that can be easily used on farms. During the experiment, 34
samples were collected from the facilities on the dairy farm at Teagasc, Johnstown
Castle (Wexford), between 27 January and 1 May, 2006. Dry matter and specific gravity
provided the best indicator of biochemical oxygen demand, total nitrogen and phosphorous,
and micro and macro nutrients. The nutrient concentration of dirty water can be
determined rapidly using either dry matter concentration or specific gravity, enabling
farmers to include this information in the nutrient management plan for their farm.