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Oxidative Treatment of Organics in Membrane Concentrates

Project: 05-10
Type: Report
Year Released: 2010

Program: Principal
Funding Partner: Bureau of Reclamation, California State Water Resources Control Board
Total Investment: $125,584.67 (Cash: $89,321.46, In-Kind: $36,263.21)

Principal Investigator: Paul Westerhoff, Ph.D., PE, Arizona State University (Tempe Campus)

Background

The use of membrane processes for wastewater treatment and reuse is rapidly expanding, especially the use of reverse osmosis (RO) membranes. RO membrane processes effectively remove organic, inorganic, and biological constituents, which accumulate in membrane concentrates. Therefore, membrane concentrates represent a significant concentrated point-source flow from the urban system into the environment. Considerable attention has focused on the impact of salts in membrane concentrates, but significantly less attention has been paid to the organic and biological constituents.

The organic materials in membrane concentrates include organic matter in the carrier drinking water, refractory chemicals added by the public to wastewater (for example, pesticides, personal care products, pharmaceutical products, endocrine disruptors, etc.), and residuals from wastewater treatment processes (for example, soluble microbial products, partially biodegraded organics, and antiscaling chemicals). Removing these organics may become important in the future as the utilization of membranes for wastewater reuse grows.

Goals and Objectives

The project developed an oxidation process for removing organics in membrane concentrates. While previous projects have focused on issues associated with inorganic salts, utilities have few resources to treat organics or microbiological organisms present in membrane concentrates.

Research Approach

Several technologies capable of oxidizing organics were evaluated: 1) Fenton reactions with and without subsequent iron coagulation; 2) ozone with and without hydrogen peroxide; 3) UV irradiation alone, with hydrogen peroxide, or with titanium dioxide; and 4) wet chemical oxidation. Oxidation experiments were conducted using bench-scale units. In addition to standard laboratory test systems, two proprietary AOP systems were evaluated. Over the course of the study, RO concentrate was collected and subjected to treatment in the bench-scale reactors. The loss of DOC as a function of chemical dosage and energy input was monitored. Changes in other organic parameters (for example, UV absorbance at 254 nm, chemical oxygen demand, and concentrations of organic acids and biodegradable components) were also monitored. During selected experiments, the steady-state concentration of hydroxyl radicals was estimated using a probe compound (para-chlorobenzoic acid).

Findings and Conclusions

Processes that produced hydroxyl radicals were capable of oxidizing DOC to purgeable gases and biodegradable organics. UV/TiO2 was selected as a sequential advanced oxidation biodegradation process because it lacks chemical reagents that could affect biological processes. UV radiation did not leave a residual, and titanium dioxide was easily separated using membranes. To achieve the 90% DOC removal goal for this project, biodegradation was incorporated, which reduced the energy dose requirements roughly by half. Thus, the project objective was achieved.

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