Characteristics and risks of secondary pollutants generation during compression and transfer of municipal solid waste in Shanghai
Introduction
Large cities like Shanghai inevitably confront the municipal solid waste (MSW) issues, which is being exacerbated by the population and economic development. The output of MSW in Shanghai increased steadily, and daily amount of waste produced is around 20,000 tons in 2010 (Huang, 2013). As a result, the city risks being overwhelmed by waste if MSW cannot be removed and properly disposed in time. Therefore, waste collection and transfer is a major challenge and should be given priority to cope with the rapid population growth, and transfer stations play an important role in waste management system, serving as a link between a MSW collection scheme and the final waste disposal facilities (Tzipi et al., 2007).
The current MSW collection and transport system in Shanghai mainly covers its subordinate districts where when solid waste are collected and transported to landfill plant for final disposal (Che et al., 2014), which usually takes several days. Organic matter in waste may be converted into wastewater and gaseous pollutants such as CH4, H2S and VOC via the action of microorganisms during waste collection and transportation (Bareither et al., 2013) when conditions are available. Highly concentrated wastewater and some flammable and explosive gaseous pollutants will cause potential environmental and safety risks if discharged without proper treatment (Zairi et al., 2014, Schwarzbauer et al., 2002). So, a necessary step of management must be urgently taken to assess the environmental quality of each transfer station according to its proximity to the inhabited area. Although many studies either have assessed the ambient air quality at landfills and incineration sites, little is known about the pollutants generations and their regular emission patterns during the MSW compression and transports process. And this could largely reduce the MSW management efficiency in Shanghai city (Campos and Zapata, 2014).
In this study, pollutants generation during compression and transfer in MSW transfer stations of Shanghai, their seasonal changes of wastewater and gaseous pollutants and the relationships between pollutant generation and operating and environmental conditions (temperature, amount of waste) were investigated. This study was a first attempt to conduct a synthetic evaluation of the secondary pollutants of the transfer station, aiming at incorporating environmental factors into a decision-making process. It is also expected to provide basic data for operation and management as well as pollution prevention and control in MSW management in the cities.
Section snippets
Characteristics of MSW in Shanghai
MSW is the mixture of a series of heterogeneous materials and usually categorized divided into organics and inorganics ones. The organics sets include food residue, wood waste, paper, textiles, rubber, and plastic (66.7%, 19.98%, 4.46%, 1.8%, 1.21% and 0.11%, respectively). Inorganics include ash (2.72%), tiles, glass (2.77%), metals (0.27%), and other inert materials. In organics MSW, the average contents of food residue, plastics, paper, textiles, wood waste and rubber were 66.7%, 19.98%,
Seasonal fluctuation of RW quality
Fig. 2 presents the seasonal variation of pH, SS, COD, BOD5, NH3-N, TN and TP of RW generated from compressing process in the three transfer stations. Fig. 2(a) shows that the average pH value of the RW collected from three MSW transfer stations fluctuated from 4.2 to 6.0 during the four seasons. The pH from HL had the lowest value of 4.3, while the highest appeared in TD transfer station, averaging at 5.5 during the whole experiment. It was observed that pH had a lower value in spring than
Conclusions
This study revealed the generation and seasonal variations of secondary pollutants during MSW compression and transfer process in Shanghai. The main results were concluded as followings:
- (1)
It is noted that RW generated from three waste transfer stations showed a high COD and BOD5 values and shared similar variation pattern during the compression process, and the concentration of TN, TP and SS were higher in summer and autumn than in winter and spring. The organics, nutrients and animal and
Acknowledgements
This work was supported by the Natural Science Foundation of China (31370510, 31411130123) and Shanghai project of international cooperation of science and technology (1352072600).
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