Sludge field

The most frequently used technique up to the present for sludge dewatering has involved the use of sludge fields, which are also used for drying, in the second stage of dewatering. 

The sludge fields are flat earth or concrete basins whose bottom is formed by dewatered filtration gravel sand. The cycle of a sludge field operation has the following stages ... 

Soil. The first reported field trial of the use of hyperaccumulating plants to remove metals from a soil contaminated by sludge appHcations has been reported (103). The results were positive, but the rates of metal uptake suggest a time scale of decades for complete cleanup. Trials with higher biomass plants, such as B.juncea, are underway at several chromium and lead contaminated sites (88), but data are not yet available. 

Field Investigation and Evaluation of Eand Treating Tannery Sludges, EPA/600/52-86/033, United States Environmental Protection Agency (EPA), 1986. 

Septic Tank Untreated liquid household wastes (sewage) will quickly clog your absorption field if not properly treated. The septic tank is a holding tank in which this treatment can take place. When sewage enters the septic tank, the heavy solids settle to the bottom of the tank the lighter solids, fats and greases partially decompose and rise to the surface and form a layer of scum. The solids that have settled to the bottom are attacked by bacteria and form sludge. 

Phosphate is sometimes present in MU water sources (say, 1-2 ppm or more) usually as a result of field and factory run-off or from the deliberate addition as a city water threshold agent to prevent corrosion and deposition in the mains. The steady growth in the reuse of secondary water sources such as municipal and industrial waste waters means that phosphate is increasingly likely to be present in MU. If the phosphate remains undetected, it likely will scale and foul FW lines by forming amorphous calcium orthophosphate [tricalcium phosphate Caj(P04)2] sludge before it reaches the boiler section. 

Field, J. and Sierra, R., Anaerobic granular sludge bed technology pages. Available at http //www.uasb. org/discover/agsb.htm. 

Industrial treatment plants may not be able to use their biological sludges as fertilizer or spread them on nearby fields if certain substances are present. They may be forced to dry and bum them instead. In some cases, as when heavy metals are present, they may have no recourse but to recover them or use deep-well or ocean-dumping methods. Often anaerobic digestors are used to reduce the amount of sludge and hence the size of subsequent equipment or the cost of ultimate disposal. 

For the field study, sewage sludge from a local municipal water treatment plant was added to a field (sandy soil) at the rates of 0, 23, 46, 92, and 184 tons/ha. Lettuce was planted after six months of sludge application. Soils were taken at the end of the field experiment (about 8 months of sludge application) (Banin et al., 1990). 

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