Common options for sludge disposal and their major advantages and disadvantages are given in table 5.

Table 5: Sludge disposal systems and their advantages and disadvantages

Land application is likely to remain as a mayor option for the future, particularly for smaller plants in rural areas which are generally less contaminated by toxic compounds and close to disposal sites. However, agricultural use is subjected to a great variability over time, depending on crop type and weather conditions while sludge production is continuous. For this option, the presence of pathogens, heavy metals and organic contaminants is important. Risks from pathogens can be properly reduced by applying available technologies but costs vary widely depending on product quality criteria, local, social and economical structure. Heavy metals and organic micropollutants arise mainly from chemicals used in industry and households. They can be controlled through cleaner technologies, reduced use and spillage and processes in the treatment works

If agricultural utilisation is taken into account, impact on the Environment and population has to be minimized by

• limitation of the applied amount

• further limitation of the applied amount according to the crop’s nutrient demand

• restrictions for sludge rich in heavy-metals

• restricted access to farmland where biosolids have been applied for 30 days

• limitation of application to even areas (< 5 % slope)

• no application close to water bodies

• soil depth to groundwater > 1m

• setback distances to water supply wells (> 150 m) and surface water supply

intake (> 750 m)

• pathogen reducing treatment (thermophilic processes, composting, humification)

• restrictions for the harvesting of crops and turf

As well as for water reuse applications, utilisation of Sewage sludge can be a problem of acceptance in the society. For further information about public awareness see lesson E3.