Abstract:
As the largest WWTP in Shanghai of China, Bailonggang WWTP is now generating 204 tons dry solids/day. 8 egg-shaped digesters (12,400 m3/each) have been installed with biogas treatment and reuse for digester operation and sludge drying. A philosophy of energy supporting for sludge digestion and drying has been applied for the design. The data obtained during the commissioning stage of this facility show:
• Relatively low solid input to the digesters;
• Remarkable variation of VSS during the wet season and dry season;
• A comparable biogas generation rate with sludge generation rate in Europe and America;
It is believed that a relatively long retention time of sludge in digester gives flexibility to operator for the optimization of digesters in this facility.
Energy balance estimation has been made, and shows that during the summer season, sludge drying process could be operated under its designed full capacity; however, during the winter season, only two sludge drying lines could be operated by using the biogas generated from digesters.
Key words:
Anaerobic digestion, Bailonggang WWTP, Biogas, Energy recovery, sludge drying
Introduction:
Shanghai is the China’s largest economic center with its trading port. It is also the largest comprehensive industrial city and the country’s major technology center, financial and information center. With the acceleration of urbanization and the development of economic construction and rapid population growth, urban sewage discharge increase rapidly. By the end of 2010, there are 53 wastewater treatment plants with a total treatment capacity of 6,840,500 m3/day. The sludge produced by these WWTPs is about 3800 tons sludge/day with a water content of 80%. Only 4% of the sludge is dealing with drying and incineration, while 7% of the sludge using composting and 3% of the sludge using for artificial materials such as coal. The major part, 86% of the sludge is treated with thickening and dewatering and finally by landfill disposal.
To solve the problem of sludge disposal, to prevent secondary pollution, maintain a good ecological environment, improve resource utilization, and promote the development of circular economy and the eco-city construction, the last two years, our related government departments promulgated a series of sewage sludge standards for landfill, landscaping, farm, etc. , also developed a series of sludge treatment and disposal technology policy, technical guidelines and technical standards, to guide the planning, design, environmental assessment.
In order to implement state requirements for sludge treatment and disposal, to solve the Shanghai municipal sewage sludge treatment and disposal problems and prevent secondary pollution, the Shanghai Water Authority in October 2009, promulgated the urban sludge treatment disposal plan, specify the urban sewage sludge treatment and disposal methods and the corresponding the technical routes.
The plan draws on the successful experience of international developed cities, in conjunction with characteristics of Shanghai urban water environment, in order to determine shanghai major sludge disposal methods, including building materials after sludge incineration, land application after sludge stabilization and sanitary landfill after sludge volume reduction.
According to the sludge plan, in the short term the total sludge treatment scale is 638 tds / d, in which the sludge treatment scale of the downtown of Shanghai is 426tds /, including
• Shidongkou sludge plant adopting drying + incineration with the treatment scale of 72tds / d,
• Zhuyuan S sludge plant adopting drying and incineration with the treatment scale of 150tds/d,
• Bailonggang sludge plant using anaerobic digestion and drying process with the treatment scale 204tds/d.
Currently Bailonggang sludge treatment project has been completed and is in the phase of commissioning and trial operation, planned operational by the end of 2011. Zhuyuan sludge treatment project is in the construction phase, and put into operation in 2014, Shidongkou sludge treatment project is in the feasibility study stage, the project put into operation in 2014.
This paper introduces engineering design, commissioning and operation, energy balance of anaerobic digestion and drying at Bailonggang WWTP, and discusses the problems encountered.
