Canada-China partnership constructs a SBR system
in Shanghai

Paper mill must meet China's stringent regulations

The Shanghai Xin Lun Paper Co. Ltd., located in Shanghai Province, China, required secondary wastewater treatment to meet the regulated effluent requirements for its recycle paper mill. They also needed a treatment system to be installed and operating when a new paper machine was brought on line in August 2000. The paper mill produces a latex-coated linerboard from recycle paper.

Regulations meant the mill had to meet a stringent effluent COD limit of 100 mg/L (other effluent limits are 30 mg/L BOD and 200 mg/L TSS). There are no COD limits on pulp and paper effluents in Canada, but limits on effluent COD are the norm in Asian countries. Limits on BOD and TSS are not as significant as COD with respect to the design and operation of the wastewater treatment plant.

ADI-SBR basin during aeration. The batch-fed SBR maximizes COD removal.	A sign at the plant reads "Environmental Protection -- Everyone's Duty", a good slogan in any language.

Several secondary treatment alternatives were considered, but in order to produce the lowest possible effluent COD, the mill selected the ADI-SBR (sequencing batch reactor) system. This batch-fed SBR eliminates short-circuiting of untreated effluent to the sewer and maximizes COD removal efficiency.

Mill expansion in the future will include a de-inking process and a second paper machine. Therefore, expandability of the wastewater treatment plant was also a consideration during the technology selection. The fact that an SBR system can be easily expanded by the construction of new basins, as needed, was a determining factor in its selection.

A contract between Shanghai Xin Lun Paper and ADI Systems Inc. was signed in January 2000. ADI supplied the process design, assisted with equipment and site layout, and supplied equipment including its proprietary stainless steel decanters, fine bubble aeration system, selected control valves and nutrient metering pumps, control logic diagrams and start-up assistance.

Partners on the project included the mill, which provided project and construction management, Changsha Designing Institute of Light Industry for detail design, and Hunan Systems Computer Company Limited for programming. ADI also participated in the planning and layout of the future expansion of the wastewater treatment plant.

Present design wastewater characteristics are tabulated below:

Flow, average 15 000 m³/d

COD, average 800 mg/L

BOD, average 400 mg/L

TSS, average 400 mg/L

Construction was carried out on a fast-track basis starting in May 2000 with substantial completion by August 2000. The plant was started up in September 2000.

The treatment system includes coarse and fine screening, pumping station, primary clarifiers, equalization basin, pumping station, and nutrient addition system. It also includes an SBR comprised of two 10,800 m³ basins and centrifugal blowers for supplying air to a grid of fine-bubble, sock-type diffusers, and a combined primary/secondary sludge dewatering facility (belt filter presses).

A design feature is the energy-saving aeration system. Each SBR is equipped with a fine-bubble diffuser grid and an on-line dissolved oxygen sensor. Fine-bubble diffusers have demonstrated an excellent efficiency in transferring oxygen from the air to the process water. This minimizes the volume of air that has to be compressed to meet oxygen demand.

Additionally, each centrifugal blower is regulated by control valves on the suction side of the blowers. As oxygen demand increases or decreases, the blower power draw is increased and/or more blowers are brought on-line. Alternatively, as oxygen demand decreases in the basins, the number of operating blowers is automatically reduced to a minimum, and the power draw on these blowers is also minimized.

Average SBR influent and effluent characteristics over a two-week test period immediately after the system was placed in automatic operation in November 2000 is summarized in Table 1.

BOD₅ of the effluent has ranged between 5 and 15 mg/L. Furthermore, during this period of relatively low organic loading, only one blower was running, and it was usually running at minimum power consumption.

Each SBR basin measures 30 m by 60 m, with a 7 m wall height. Up to four hundred labourers worked on leveling the floor of each basin when the concrete was continuously poured over a 24-hour period. ADI Systems Inc. had designed and installed a similar-sized SBR system for the pulp and paper industry in Canada, and were very impressed with the speed and quality of work in China.

The system is automatically controlled by a PLC system with a personal computer operator interface. All control screens are bilingual (Mandarin and English). Plans are in place to install a telephone line to the control computer. This will allow access to process specialists at ADI offices in Canada, so that the system can be monitored remotely to assist in troubleshooting operations as flows and loadings increase.

It is envisioned that a second paper machine will approximately double the flow and loading. The pretreatment system is sized for this future flow scenario, and plans are in place to install an additional two identically sized SBR basins.

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