Disposal pits and deep row entrenchments are meant for sludge originating from households. It is imperative to note that no industrial, commercial, or toxic sludges should be disposed of using these methods, especially without the installation of a liner system. Detailed records should be maintained, documenting the sludge’s source, pre-treatment it has undergone, and the quantity deposited. Ideally, sludge deposits in trenches or pits should be avoided during the rainy season.
Sampling and Quality Assurance
Sampling of deposited sludge should be conducted any time there is reason to believe that sludge quality has changed, or sludge may have an increased level of pollutants. The safety of groundwater is of utmost importance.
Test Boreholes and Baseline Values
Test boreholes should be installed 30 to 45 m from the disposal site. Water samples should be taken from the test boreholes and other water sources nearby prior to disposal to establish baseline values. These boreholes should be used to periodically take water samples that are tested and compared with the baseline values to ensure no contamination due to leaching.
Soil Testing and Crop Monitoring
For most crops, soil testing should be conducted every 2 to 3 years. Soil under intensive cultivation may require annual testing. Sampling from any given area should be done at about the same time as in previous years. It is also advised to monitor the treated sludge for Biochemical Oxygen Demand (BOD), Total Suspended Solids (TSS), Nitrogen (N), Phosphorous (P) and bacteria before burial or final disposal. High values increase the risk of polluting the ground and surface water sources due to leaching effects.
The following table summarizes important parameters to be measured as well as their recommended ranges for safe sludge disposal.
Parameter
Explanation
Recommended Range for Safe Disposal
pH level of soil
A measure that is important for microbial activity, waste decomposition, and prevention of adverse environmental impacts.
To be tested in soil and surrounding soil of the disposal site.
6 < pHsoil < 7 (testing once a year)
Biochemical Oxygen Demand
A measure of the dissolved oxygen required to stabilize the organic matter in five days.
To be tested in deposited biosolids.
<100 mg/L (testing once a year or when source/treatment process of biosolids undergo changes)
Total Suspended Solids
A measure of organic and inorganic solids that are not dissolved and may be removed by coagulation or filtration.
To be tested in deposited biosolids.
<300 mg/L (testing once a year or when source/treatment process of biosolids undergo changes)
Nitrogen
Valuable nutrient for crop growth. Occurs in several forms (organic nitrogen, ammonia, nitrite, nitrate). In surface water, it can accelerate the growth of aquatic plants. In groundwater, nitrate is a health threat if it enters drinking water supplies.
To be tested in the soil of the disposal area and boreholes/nearby water sources.
Nitrate in water: <50 mg/L (monthly and seasonal testing recommended)
Nitrate in soil: 10 – 50 mg/kg (testing once a year or when elevated values in water)
Phosphorous
A valuable nutrient that exists in organic and inorganic forms. Can cause eutrophication in surface water. It leads to water bodies being unsuitable for aquatic life and as a source of drinking water.
To be tested in the soil of the disposal area and boreholes/nearby water sources.
In water: 5 mg/L (monthly and seasonal testing recommended)
In soil: 500 – 800 mg/kg dry soil (testing once a year or when elevated values in water)
Bacteria
Indicates the potential presence of pathogenic organisms.
According to national regulations.
Heavy metals
Commonly regulated heavy metals include lead, cadmium, mercury, and others, which should be monitored and maintained within safe ranges to prevent environmental contamination.
According to national regulations.
Important Parameters and their Recommended Ranges Concerning Safe Sludge Disposal
For further information, please click on the Materials tab at the top of the page.
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