The majority of wastewater treatment techniques result in sludge that needs to be disposed of. A primary sludge is produced in the primary sedimentation stage of treatment, and a secondary, biological sludge is produced in the final sedimentation stage following the biological process. Secondary sludge has different properties depending on the type of biological process it is subjected to, and it is frequently combined with primary sludge prior to treatment and disposal.
Sludge treatment and disposal account for almost 50% of the operational expenses, of secondary sewage treatment facilities. In addition to meeting a sizable portion of the nitrogen and phosphorus needs of many crops, land application of raw or treated sewage sludge can significantly lower the cost component of sludge disposal, associated with sewage treatment.
But, before applying sewage sludge for agriculture purposes, we have to understand its impact on the crops.
What does sewage sludge contain?
Along with other parasitic helminths, sewage sludge also contains harmful bacteria, viruses, and protozoa that pose a risk to the health of people, animals, and plants. Salmonellae and Taenia are identified as the microorganisms posing the highest health risk in a WHO report, on the harm to health of germs in sewage sludge applied to land.
The potential health risk is further diminished by the impacts of climate, soil microorganisms, and time after the sludge is applied to the soil by adequate sludge treatment, which can greatly lower the populations of pathogenic and parasitic organisms in sludge before application to the land. However, restrictions on planting, grazing, and harvesting are required for some crops.
Sewage sludge also has beneficial amounts of nitrogen, phosphorus, and organic matter in addition to those problematic components.
What are the Impact of sewage sludge on agriculture?
Untreated liquid sludge and dewatered treated sludge releases nitrogen slowly, with the advantages to crops being realized over a relatively lengthy period of time.
Sludge treatment is more dependent on nitrogen availability. The ammonia-nitrogen content of liquid anaerobically digested sludge is high, and is easily absorbed by plants, making it particularly advantageous for grassland. When added as a dewatered sludge cake, the organic matter in sludge can enhance some soils' ability, to retain water and structure.
Constraints on planting, grazing, and harvesting
Firstly, sludge applications must be coordinated with planting, grazing, or harvesting activities, in order to reduce any potential harm to the health of people, animals, and plants. Soft fruit and vegetable crops should not be cultivated with sludge, and neither should crops grown inside of permanent glass or plastic structures.
Secondly, treated sludge can be used without restriction to produce cereal crops, however, it shouldn't be used to grow turf within three months of harvest, or fruit trees within ten months of harvest.
Thirdly, no restrictions apply when treated sludge is spread prior to the planting of crops, such as cereals, grass, fodder, sugar beet, fruit trees, etc. However, treated sludge shouldn't be applied within 10 months after crop harvesting, in the case of soft fruit and vegetables.
Finally, untreated sludge should generally only be cultivated or injected into the soil, prior to planting crops, however it is ok to do so for growing grass or turf, as long as the minimum time to harvest is met.
In crop production, sewage sludge can take the place of mineral fertilizers. The quantity and ratio of mineral elements that are available to the plant throughout plant growth, should be taken into consideration. Potassium and phosphorus may not be fully supplied to plants by sewage sludge.
Because, sewage sludge releases nutrients gradually, it is suggested for plants with extended vegetative periods. During seed germination, a phytotoxic impact could manifest.
How can we assist?
Netsol Water is a well-known and reputable water treatment plant, wastewater treatment plant and sewage treatment plant manufacturer, and supplier. Our treatment plants include physiochemical, chemical, and biological processes, to convert the sludge into fertilizer so that sludge provides a positive impact on the crops.