Research On The Performance Of Constructed Wetlands For Waste Sludge Treatment

Wastewater sludge treatment and disposal is one important aspect of wastewater treatment. While sludge with unsuitable treatment may bring in secondary pollution to environment and useful resources waste. Most wastewater treatment plants (WWTP) constructed before the year of 2000 have not waste sludge treatment facilities. In parts of WWTP, sludge digested and dewatered was applied in farmland directly, which cannot meet the standard of sludge for agricultural application. Thus energy-saving waste sludge treatment technologies with low invest and operation cost will be helpful to develop sludge treatment industry in China.Wastewater sludge compose of plenty of organic matter and nutrients such as nitrogen, phosphorus and potassium and necessary elements for plant growing such as Calcium, Magnesium, Copper and iron, which can stimulate wet plant growing. At the same time, plant growth can stimulate sludge stabilization and harmlessness. Stabilized sludge as fertilizer has the role of soil structure modification, soil function improvement and plant growth stimulation.This research in domestic proposed for the first time used for wastewater sludge dewatering and stabilization., and has conducted the experimental study.Constructed wetland technology was used A pilot-scale vertical flow constructed wetland with a surface area of 80 m~2, having 60 cm sand-gravel matrix, supported by ventilated-drainage system and planting with common reed (Phragmites australi) in the first year and about 25% of area planting with cattails (Typha augustifolia) in the second year, were fed with waste sludge from SBR process, 3rd WWTP located in Changchun city, China. The substrata in constructed wetland unit comprise a 20-cm layer of large gravel, a 25-cm layer of small gravel, a 10-cm layer of fine sand, and 10-cm layer of coarse sand from bottom to top, while a free board of 0.5 m was allowed for accumulation of dewatered sludge. The system operated from May, 2005 to November, 2006 during growing season, the performance of the system was conducted under the loading of 7m~3/4d,10m~3/4d,15m~3/4d, sludge loading ranged from 0.166 to1.213kg(TS)/m~2.d (average 0.691) or 60.6 to 442.7 kg(TS)/m~2.yr (average 252.2).The results showed that constructed wetlands played the important role to waste sludge dewatering, organic degradation and microorganisms inactivity, and accordingly to sludge stabilization. It is technically feasible to use constructed wetland technology for wastewater sludge treatment and disposal.Accumulated sludge in the system can be used for composting directly, adding planted reeds and grass as adjust and expansion. The composting product accords with the standard of sludge agricultural application. The ratio of percolate of composting sludge to distilled water range from 0.15 to 0.51, corresponding composting germination percentage is great than 50%, the maximum percentage of 89% was get under the ratio of 0.25.