A Study of the quality of Sewage sludge and municipal solid waste compost
And its Usability as soil fertilizer
Nguyen Thanh Binh
ABSTRACT
Composting of sewage sludge and municipal solid waste has long been considered an attractive
waste management option for effective reduction of waste volume. While in developed countries, a
considerable attention has been paid to utilization of these composts in agriculture, their use as a
recycled material has received comparatively little attention in Vietnam. In addition, the effects of refuse
compost applications on the soil-plant system are not yet well understood in humid tropics. Therefore,
we have focused on: (i) changes in chemical properties of sewage sludge during composting process,
(ii) the quality of compost from sewage sludge and municipal solid waste, and (iii) utilization of
municipal solid waste compost.
Three domestic sewage sludge composts (SSC) were selected from the composting plant in
Okayama pref., Japan at different stages of composting: at 8, 30 and 50 days in process. The two
municipal solid waste composts (MSC) were collected from two solid waste treatment plants in
Vietnam. SSC and MSC properties were assessed using standard chemical analysis (pH, moisture
content, Total C, organic-N, inorganic-N, Total-P, available-P and exchangeable-cations). A series of
three greenhouse pot experiments was carried out using SSC and MSC to (i) determine the optimum
rate of N and P for Italian ryegrass (Lolium multiflorum Lam.) in sandy soil, (ii) study on influence of
SSC maturity on plant growth with different rates of compost, and (iii) compare the effectiveness of SSC
and MSC on plant productivity and soil properties. An incubation and plant culture trial under combined
application of composts and chemical fertilizer (CF) (15NH4)2SO4 (13.172 atom %) with 15N-trace
technique were carried out to estimate the Gross N transformation rates and fate of N-15 to ryegrass
under controlled conditions.
Sewage sludge compost properties varied significantly between raw material and compost
product. Chemical analysis indicated high value in most nutrients; especially N and P. Italian ryegrass
dry weight and N uptake significantly increased with increasing sewage sludge compost application
rates. The application of either SSC or MSC is likely to improve significantly soil quality, by increasing
soil total N and C: N ratio. Under combined application of MSC and low level of CF, about 33.1 and
47.0 mg N kg-1 day -1 soil from the initial inorganic- 15N pool was immobilized during 10 days of
incubation at 25°C and 35°C, respectively. During the same time, about 16.6 and 31.3 mg kg -1 day -1
soil from organic 14N pool was mineralized at 25°C and 35°C, respectively, suggesting that both
mineralization and immobilization rates increased with temperature. However, with higher level of CF
combined with MSC, the amount of N immobilized increased by 17% and the amount of N mineralized
decreased by 41 % in comparison to low level of CF addition, indicating that a microorganisms
competed with more available N. These results also corresponded with ryegrass yield depending on the
level of N from CF combined with MSC. Under SSC + low level of CF treatments, about 45% of total
nitrogen in plants derived from chemical fertilizer source and 55% derived from compost + soil. On the
contrary, under MSC + CF treatments 54% of total nitrogen was derived from chemical fertilizer source
and 46 % derived from compost + soil. Single application of SSC was confirmed for obtaining high
yield, results from combined application of MSC with N improved materials may enhance compost
quality and therefore require further investigation.
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