Abstract
Mixture of sewage sludge with organic garbage was alternatively composted by aerobic and anaerobic technology for 60 days. A basin-scale experiment was performed by planting watercress with kailyard (KY) soil amended with the compost. The results show that average total organic carbon (TOC) increases from 98.45% to 787.69%, and average total nitrogen (TN), total phosphorus (TP) and total potassium (TK) increases to 98.53%, 27.34%, and 41.62%, respectively. The results of watercress in 6 pot experiments with a control treatment show that biomass production increases from 76.47% to 312.00% with the increase of addition of compost from 50 g to 150 g per pot but decreases from 312.00% to 102.29% with the addition of compost to soil and further increases from 150 g to 400 g per pot. The optimal amount of compost added to KY soil is 0.4 g of compost 1 kg of KY soil. Heavy metals accumulated by watercress demonstrate that Cu, Ni, Cd, Pb, Cr, Zn in the crop are much lower than the limited levels of Chinese criteria for vegetables. KY soil is proper to be amended with compost of sewage sludge without threat of bio-magnification of heavy metals to planting watercress.
Introduction
Sludge is one of the principal byproducts of wastewater biologically treated by activated sludge methods or bio-film methods in wastewater treatment plants (WWTP). Each year China generates approximately 1.3 billion kilograms of sewage sludge and this figure is still increasing (Hang et al., 2005). The high annual production of sewage sludge causes a series of economic, social and contamination problems. One of the key problems that China has to face directly is the disposal problem of the increasing sludge. A number of methods of sewage sludge disposal have been proposed and implemented, including landfill, incineration, sea disposal and composting. Ocean disposal of sludge is currently forbidden. Landfilling of sludge has been another inexpensive method of disposal but needs more filling land. Incineration reduces sludge to ash, which can then be used for landfilling, but in most cases, supplementary fuel is needed to burn sludge, which makes this method less economical (Dolgen et al., 2007). Composting, which is of a solid fermentation biotechnology for the treatment of organic solid wastes, can convert sewage sludge to compost which can be used as fertilizer for bioremediation of soils (Zhou, 2003). As a soil conditioner in farmland, forests and home gardens, use of sewage sludge in crop production is ideally favorable for a sustainable society, as it can recycle a substantial content of nutrients and organic matters (Ahlberg et al., 2006).
Write only the main points and their gaps finding and difficulty they found in studies needs for future research studies
Main points:
1. Mixture of sewage sludge with organic garbage can be composted using aerobic and anaerobic technology.
2. Composting increases the total organic carbon, nitrogen, phosphorus, and potassium content of the compost.
3. Watercress planted in soil amended with compost shows increased biomass production.
4. Heavy metals accumulated by watercress from compost-amended soil are below acceptable levels for vegetables.
Gaps and findings:
1. Optimal compost addition to soil is 0.4 g of compost per 1 kg of soil.
2. Heavy metal accumulation in watercress from compost-amended soil is not a threat.
3. Future research is needed to investigate the long-term effects of compost-amended soil on crop production and soil health.
4. Further studies should evaluate the potential risks of using sewage sludge compost on a larger scale and in different types of crops.