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Analysis of Parameters Affecting Process Efficiency, Energy Consumption, and Carbon Footprint in Water Reuse

Project: 08-11
Year Released: 2015
Type: Scientific Investigation

Program: Principal
Funding Partner: Bureau of Reclamation
Total Investment: $499,997 (Cash: $119,997, In-Kind: $320,000)

Principal Investigators: Kenneth P. Ishida, Orange County Water District, and Dr. William J. Cooper, University of California Irvine

Background

Improvements in the operation of MF, RO, and UV/AOP of the Advanced Water Purification Facility are desired. However, a thorough understanding of the mechanisms of fouling, and the chemical nature of their foulants are needed. Similarly, a detailed understanding of the UV/H2O2 advanced oxidation process is lacking. This data along with a carbon and energy footprint analysis were used to develop monitoring and control strategies to optimize the performance of the processes of the wastewater recycling facility

Goals and Objectives

This research project was divided into five major objectives with the majority of the objectives directed toward the characterization of MF and RO fouling mechanisms, the characterization of the MF foulants, and the characterization of the UV/H2O2 AOP. From these studies strategies could be identified to improve on the performance of the AWPF. For the first time since the startup, a carbon and energy footprint analysis of the AWPF was conducted.

Research Approach

A number of standard and nonstandard analytical methods were used to characterize (1) the organic matter in the feedwater to the MF process, (2) foulants on the MF hollow fibers, (3) foulants on the RO membrane surface, and (4) trace organic and inorganic constituents in the RO permeate and UV/AOP product water. These methods included gas chromatography, mass spectrometry, excitation-emission matrix fluorescence spectroscopy, ATR-FTIR spectroscopy, 1H NMR spectroscopy, and SEM-EDX spectroscopy. The project team designed experiments and collected and analyzed data from bench-, pilot-, and full-scale units to characterize the MF, RO, and UV/H2O2 processes of the AWPF.

Findings and Conclusions

One of the major objectives of the project was to determine the fouling mechanism and characterize the foulants associated with the MF and RO processes. Removal of nanoparticle effluent organic matter with an aluminum-based coagulant resulted in significant lengthening of the cleaning interval of the MF membranes.

The relationship between the accumulation of biological, organic, and inorganic matter on the RO membrane fouling was investigated for each stage of the three-stage RO process. In the first stage, fouling was best related to the accumulation of protein material on the membrane surfaces. In the second stage, this relationship transitioned to accumulation of viable aerobic heterotrophic bacteria. And finally in the third RO stage, fouling was initially influenced by the presence of viable bacteria at the beginning of the stage but transitioned toward an “uncharacterized factor” at the end of the stage.

A dynamic energy footprint model of the MF/RO/UV/AOP was generated. The results showed the benefit of an adaptive MF backwash cycling (determined from the dynamic influent load), and revealed the significant variation in required power for RO pumping in a regular diurnal period. Furthermore, an analysis of the indirect greenhouse gas emission associated with the operation of the AWPF indicated that these emissions are dominated by those associated with electricity consumption, i.e. 95–97% contribution, compared to the emission associated to chemical transportations, i.e. 3–5% contribution.

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