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5.5.1 On-site Sludge Management
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5.5.1 On-site Sludge Management

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The on-site management of sludge is a feasible and cost-effective method for rural villages. Sludge drying beds are the most common and easily managed method for sludge drying and treatment. A sludge drying bed is a simple, permeable bed that, when loaded with sludge, collects percolated leachate and allows the sludge to dry by evaporation. Approximately 50% to 80% of the sludge volume drains off as liquid back to the treatment plant. A drying bed system usually includes at least two drying beds, used alternately to make sure the solids are adequately dried and stabilized before the sludge is removed. The bottom of the drying bed is lined with an impermeable liner or concrete and has a perforated pipe on the bottom to collect and convey leachate back to the treatment process. Above the pipes are layers of gravel and sand that support the sludge and allow the liquid to drain freely to the underdrain pipe. When the sludge is dried, it can be used as an organic soil additive or added to compost for additional treatment if it does not contain any contaminants, such as heavy metals.  In cold and/or wet regions, the sand bed can be either installed in an enclosure or under a roof to minimize inundation from rainfall.

   

The indicative capital costs for sludge treatment facilities in concentrated rural wastewater treatment stations/plants are shown in Table 5.3.

 

Table 5.3 Indicative costs for onsite sludge treatment facilities

Process

Cost per ton wastewater (RMB)

Capacity

<100 m3/d

(wastewater volume)

Capacity

101-500 m3/d

(wastewater volume)

Capacity

501-1000 m3/d

(wastewater volume)

Capacity

1001-5000 m3/d

(wastewater volume)

Sludge dewatering

520-1300

260-520

220-260

160-220

Sludge drying

260-520

240-260

190-240

130-190

Sludge digestion

390-650

390-580

350-520

320-490

Sludge composting

160-190

130-160

100-130

90-100

Source: Guideline for Construction and Investment of Rural Domestic Wastewater Treatment Project (2013)

 

  

  

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