MSWI Bottom Ash Properties Variation Under The Influence Of Weathering And Phytoremediation

In this experiement the initial p H value of MSWI(Municipal soild waste incineration,MSWI) bottom ash was 12.79. It contained a variety of heavy metals, including Zn, Cu, Pb and Cr.Their contents were 3452mg/Kg, 2316mg/Kg, 222mg/Kg and 327 mg/Kg respectively. In order to study the characteristics of bottom ash under different conditions, this paper studied the changes of the different nature of the cultivated substrate, which were treated by MSWI bottom ash and soil. The experiment was divided into 6 groups named No.1 to 6, which the weight ratio of bottom ash was 0%, 20%, 40%, 60%, 80% and 100% respectively and other component was soil. The 6 groups cultivated substrates were experienced 4 stages. They were called the.first time to plant(0th to 4th week), natural weathering( 5th to 15 th week), the second time to plant(16th to 20 th week) and the third time to plant(21st to 35 th week).Sample and carry out extraction test at 0th week,15 th week,25 th week and 35 th week. At the start,the p H value was higer if the cultivated substrate contained more bottom ash. After weathering, the p H value drop of No.2 to No.6 cultivated substrate was more than 1.5. Compared with last period, the p H value of No.1 to 6 was decreased by 0.25, 0.34, 0.29, 2.35, 1.93, 2.96 at 25 th week respectively. At the end of the experiment, the p H value of them was decreased by the range.from 0.05 to 0.34. The COD value of the substrate in each group also showed a decreasing trend. After weathering, the value of different substrates dropped at the range.from 20 to 42 mg/L.After planting, the COD value drop of No.1 to 6 was more than140mg/L. It showed that the effect of growing plant on COD was more than that of weathering. The electrical conductivity of No.1 and No.2 substrate was increasing all the time.However, No.3 and No.4 substrate was increasing from the 0th to 25 th week, but it decreased at the end of the experiment. The value of No.5 and No.6 substrates was drop after weathering. Afterwards electrical conductivity of No. 5 was up then down however No.6 was increasing. The oxidation reduction potential of each cultivation was increasing from the 0th to 25 th week then decreased, but still higher than the initial value, and the higher value of No.1 to No.6 were 14, 56, 79, 92, 114 and 135 m V respectively.The TN content of each cultivation substrate decreased obviously with weathering,but it increased more significantly than the first with watering Hoagland nutrient solution.However, the content of ammonia nitrogen decreased all the time. The change trend of TP in different cultivation substrate was not same. The value of No.2 to No.6 substrate from the 0th to 25 th week showed a downward trend, and then a rising trend except for No.1.The number of microbial population in cultivation substrate.after weathering was 11.They were ascomycetes,Mycoplana sp,Arthrobacter sp., Acinetobacter Acinetobacter sp., Pseudomonas sp.and so on. At the end of the test, it dcreased to 4. The microbial numbe of No.3 and No.5 cultivation substrate was reduced by 1 orders of magnitude.However, No.4 substrates decreased by 2 orders of magnitude and the number of other substrates always decreasedBrassica juncea and Medicago sativa grew badly except the No.1 cultivation substrate before weathering. After weathering,they grew better and the heavy metals enrichment coefficient of Brassica juncea and Medicago sativa in soil were higher than other cultivation substrates which contained bottom ash. The Brassica juncea in cultivation substrates which contained bottom ash had a higer enrichment coefficient of Zn and Pb than Medicago sativa.However, Medicago sativa had an more obvious enrichment effect on Cu, Cr and Ni.It planted Sedum alfredii from 21 th week to 35 th week.The heavy metal enrichment coefficient of Zn, Cu and Pb in No.1 substrate was higher than other all the time and decreased with growth cycle increasing. In the whole growth cycle of Sedum alfredii, plants in No. 2 substrate had a higher heavy metals enrichment coefficient among No.2 to No.6 substrate.In 6 groups, Sedum alfredii in No. 6 substrate absorbed Zn, Cu, Pb and Cr most and No. 2 substrate absorbed Ni most in total.