Technology with the Environment in Mind

Novel Wastewater Reclamation Technology Meets Environmental and Business Challenges

MEMBRANE BIOREACTOR PERFORMANCE AND Applications To Further Water Reuse

Background

The semiconductor industry uses ultrapure water (UPW) to rinse impurities from the wafer surface. Once contaminated with dissolved and suspended solids, organic and ammonia nitrogen, and multiple organic compounds, most semiconductor manufacturers discharge their wastewater offsite to municipal treatment plants, where these contaminants are removed. Although some companies reclaim some of this water for facilities applications (e.g., scrubbers, cooling towers), most UPW is treated as a "once-through" opportunity, limiting possibilities for water conservation.

MBR technology is not new and has been proven in many applications for organic, suspended solids and nitrogen removal. The technology development team quickly noted that effluent from the pilot plant was producing water comparable in quality to city water and might be suitable to replace city water in the UPW system feed. This was consistent with the data in literature that indicated that the MBR was quickly gaining recognition as the most effective process for treatment of industrial wastewater. In many cases, the MBR has been proven to produce very high-quality effluent suitable for almost unrestricted recycling. In fact, some U.S. states (e.g., Oregon) are currently revising their rules for reclaimed water to classify MBR effluent as Level IV reclaimed water, the highest purity classification available [13].

Semiconductor Wastewater Characteristics

Data in the literature indicates that the typical industrial effluent from semiconductor plants has the following characteristics, listed in Table 2.

Table 2: Characteristics of semiconductor plant effluents
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Of the organic compounds typically used in semiconductor manufacturing, the compound used in the new plant had been reported to pose a problem for biological treatment. Although the organic compound can be biodegraded by certain strains of bacteria [7, 10] its biodegradation in conventional wastewater treatment systems was reported to be slow and incomplete [5, 11]. For this reason, both total organics degradation and the removal efficiency for this particular organic compound were evaluated.

Organic matter (shown as COD and BOD in Table 2) has been demonstrated to severely reduce the performance of RO membranes [3]. Therefore, effective removal of organics is also critical if treated effluent is to be reused.

MBR Pilot Operation

The MBR pilot was operated at an Intel Technology Development location for 14 months. The pilot system treated 1.8 gpm of the combined effluent from the factory and consisted of aerobic and anoxic biological reactors followed by the membrane module. Pretreatment was accomplished using an ultrafilter (UF) module utilizing hollow-fiber membranes operated under vacuum. Additionally, 100 mg/L of the problematic organic compounds were added to the waste stream over the entire period of operation to simulate worst-case conditions.

Analytical

The pilot was equipped with an on-line system for measuring turbidity in the final effluent. Suspended solids, oxidizable organics, and nitrogen (ammonia nitrogen, organic nitrogen, nitrates, and nitrites) were measured in both waste stream and treated effluent. In addition, Total Organic Carbon (TOC) was periodically measured using a TOC analyzer. Tests were performed in accordance with Standard Methods [1]. For the compound in question, concentration in the treated effluent was measured by a vendor using a proprietary method.

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