Technology with the Environment in Mind

Novel Wastewater Reclamation Technology Meets Environmental and Business Challenges

RESULTS

Treated Effluent Quality

Biological Oxygen Demand (BOD) tests are typically used to measure organic matter content in treated wastewater. However, these parameters cannot be directly translated into a concentration of organics if the exact chemical composition is not known. For this reason, TOC measurements were also conducted.

Analyses of data from the pilot operations indicated stable and effective removal of nitrogen compounds, organic matter, and suspended solids to levels lower than required (Table 1). In addition to nearly complete removal of organics and TKN, complete biodegradation of the other organic compound was confirmed by direct measurements. In all samples the concentration was below the detection limit of 4 mg/L.

Several projects have recently reported the feasibility of reuse of biologically treated municipal wastewater. Most of the systems included microfiltration (MF) followed by RO [12, 9]. A range of treated wastewater parameters from the literature, for which MF/RO treatment was successfully implemented, is shown in Table 3.

Table 3: Treated wastewater quality parameters
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MF pretreatment was needed to remove suspended solids that were present in the treated municipal wastewater, as evidenced by the effluent turbidity. Data in Table 3 suggest that combined effluent of a semiconductor Fab can be treated to achieve a quality exceeding that reported in other successful water reuse projects. Low turbidity values observed in this study are due to the fact that MBR utilizes UF for biomass separation, and that effectively removes all suspended solids and potentially eliminates the need for RO pretreatment. In fact, RO was successfully applied directly to the MBR effluent in several previous studies [2, 4].

Cost Considerations

Water reuse concepts ranging from irrigation to UPW recycle as described in this paper can be implemented at competitive cost, providing both monetary and resource conservation benefits. The feasibility of this approach can only be determined on a case-by-case basis. The following considerations must be taken into account in the cost/benefits analysis:

Costs

• Capital cost of the MBR.
• MBR operating cost.
• UPW system upgrade if the existing system does not have the capacity to operate at reduced recovery rate.
• Higher volume of RO reject.

  Benefits

• Environmental protection and water conservation.
• Greatly reduced dependency on local infrastructure.
• Reduced water bill and wastewater treatment fee.
• Reduced use of RO pretreatment systems, since MBR effluent can be directly fed to RO.
• In some cases, MBR may eliminate the need for certain waste treatment systems (e.g., ammonia, solvents, waste neutralization), thus fully or partially off-setting the capital cost.
• Reduced dependence on availability and quality of local water supply.

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