According to the popular definition, wastewater is defined as used liquids, solutions, colloids or suspensions, as well as waste solids discharged by means of pipelines into sewers, septic tanks, treatment tanks or watercourses. Industrial and municipal waste substances from households are discharged as wastewater. Wastewater thus arises as a result of domestic or production processes and, by definition, is directed to a wastewater treatment plant, where it is treated before being discharged into the environment as relatively clean water. However, agriculturally contaminated water can be a valuable raw material in the food production process.
Various types of wastewater and waste water can be generated on the farm. These include domestic wastewater, leachate from animal production, which is organic fertiliser and crop production (silage leachate), and washings from the washing of farm equipment, facilities and buildings.
While domestic wastewater can be managed fairly easily (municipal sewers, septic tanks), the use of waste water generated by agricultural production requires some investment and operational discipline. Liquid and solid organic manures must be collected and stored appropriately, taking care to limit the volume of any leachate and to collect it carefully in appropriate tanks for management. Failure to collect and utilise leachate results in the loss of nitrogen and other valuable nutrients, e.g. silage sludge run-off from 25 tonnes of ensiled green matter (average yield per hectare) contains up to 14 kg of nitrogen, which, if it enters surface waters, will pollute them and deprive the water of oxygen. Efforts should therefore be made to minimise the amount of leachate generated and to collect the leachate that has already been generated and use it for fertiliser or another form of biological neutralisation.
Households with a water supply use considerably more water than households using their own water intake (well), resulting in increased sewage and waste water. These households should be connected to a collective sewage system or have a domestic sewage treatment plant.
According to the Good Agricultural Practice Code guidelines, farms with an individual water intake should have a sealed tank for the temporary collection of domestic sewage. The tank should have a sealed lid with a lockable opening for the disposal of waste water. Non-returnable tanks – septic tanks – should be emptied using septic tankers and the contents delivered to the nearest sewage treatment plant. Sewage must not be discharged directly into surface water, groundwater or spilled on fields.
In the course of production operations, a number of agricultural washings are generated from the washing of vehicles, equipment, tanks, buildings, etc. While the wastewater must absolutely be transported to a treatment plant, the washings, which do not contain substances harmful to plants and animals, can, after the necessary treatment, be released into the environment in accordance with the water law permit, or be managed in the manner in which organic liquid fertilisers are used.
On the farm, particularly harmful substances enter the water when washing tractors, fertiliser spreaders and sprayers, including various organic compounds (fuel, lubricants, chemical plant protection products) and mineral fertilisers. Therefore, the farm should have a washing plant with a neutraliser for washings that cannot be cleaned by separation or used in further agricultural production.
An often neglected topic is water run-off from paved yards and roads on the farm, which can carry harmful substances, especially oily substances. According to the law, the solids and also the oily parts must be separated from it, as only in this state can it be released into the environment in accordance with the water permit.