Biomass And Pollutant Content Of Plant Grown In Soils Amended With Sewage Sludge Compost

With the increasing number of wastewater treatment plants,more and more municipal sewage sludge(SS) is produced.Due to the absence of sound treatment method,most of the SS was piled in temporary places and becoming new potential pollution sources.There is an urgent need for a safe disposal option.Land application of SS is seen as one of the best options.The cost-effective and beneficial effect of SS as plant nutrient source is promoted.The dire with SS application is the presence of inorganic and organic pollutants that affect the quality and quantity of plant yield. Composting has been proposed as one solution to reduce the contaminants and improve the quality of SS.Thus in this study,we investigated the potential use of sewage sludge compost(SSC) in soil and its effects on plant uptake of pollutants from SSC.Plant growth experiment was performed to compare the growth of Chinese cabbage(Brassica chinensis),radish(Raphanus sativus),2 turf grasses ryegrass (Lollium perenne) and fescue grass(Festuca ovina) in soil amended with SSC versus SS.After composting,a yellow loamy soil and a red soil were amended with SSC at different application rates for the growth of vegetables and turf grass.Addition of SSC could significantly increase the TN,TP,urease,electrical conductivity(EC) and cations exchange capacity(CEC) in soil.DTPA-extractable Cu and Zn in soil increased significantly according to the SSC application rate.Biomasses of all tested plants were improved with the addition of SSC.At 10%SSC,yield of Chinese cabbage increased 40%and 73%in yellow and red soil compared to optimal with SS. Yield of radish also increased for about 36%and 40%in the soil.In ryegrass,adding 40%SSC in soil increased the yield for about 51%and 121%in red and yellow soil, respectively.Apparently,ryegrass is more resistant to high rates of SSC and SS than fescue regardless of the soil type.In regard to the results,applying SSC improved the yield of tested plant more effectively than SS.Therefore,using SSC as soil amendment should be recommended rather than SS.Effect of SSC amendment in soil on the Zn and Cu content in turfgrass and Chinese cabbage were investigated.SSC amendment increased the level of Zn and Cu in plant tissue.In rescue,concentrations of Zn at 80%SSC application rate increased 82%and 79%compared to the control in red and yellow soil,respectively.In ryegrass, it was 80%and 77%in red and yellow soil,respectively.As for Cu,in rescue grass, also at 80%SSC application rate,concentrations increased for about 58%and 67% compared to the control in red and yellow soil,respectively.It was about 50%in both soils for ryegrass.Ryegrass shows a better resistance to metal stress than rescue.Zn and Cu concentrations in turfgrass increased significantly with SSC amendment. Therefore,the grasses should be recommended for greenery rather than animals graze. The trend of Cu and Zn in Chinese cabbage were completely different between the two kinds of soil.Cu and Zn uptake increased slightly with the increasing amount of SSC in yellow soil.In red soil,however,it increased dramatically.In Chinese cabbage, Zn increased 74%in red soil and 47%in yellow soil at 10%SSC application.For Cu, concentration increased 77%in red soil and 19%in yellow soil for the same rate. Although levels of Zn and Cu increased in Chinese cabbage,they were still below the toxic limit for consumption.PAHs contents in turfgrass,Chinese cabbage and radish grown in soil amended with SSC have also been accessed.PAHs uptake by tested plants increased with the addition of SSC.It was slightly lower in yellow soil than in red soil.Ryegrass uptake of PAHs was slightly higher than in fescue.In turfgrass,sum of sixteen vary from 0.315 to 2.037 mg kg^-1.In vegetables,it varies from 0.405 to 1.27 mg kg^-1. Individuals' carcinogenic PAHs were all under detectable.2-4 rings PAHs were prevalent.In general,sum of sixteen PAHs were higher than the level in vegetables reported abroad but close to the level in vegetable find in China mainland.Even though composting has reduced the bioavailability of heavy metals and PAHs in the sludge,using high rate of SSC for food crop production is not recommended.Thus rational use of SSC can take advantage of its beneficial effect as a nutrient source for plant production while avoiding the potential hazards effects on plant.