Impacts of Membrane Process Residuals on Wastewater Treatment
Project: 02-06 (Phase C)
Type: Decision Making Tool
Year Released: 2008
Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board, Water Research Foundation, Water Environment Research Foundation, City of Phoenix
Total Investment: $435,844.24 (Cash: $395,000, In-Kind: $40,844.24)
Principal Investigator: Alan E. Rimer, Black & Veatch
Background
As the use of membrane processes in the treatment of drinking water is rapidly expanding worldwide, their application in water reuse projects expands as well and will be equally important. Membrane technologies that are used to remove inorganic ions (reverse osmosis, nanofiltration, and electrodialysis) produce a residuals stream that is enriched in such ions. The stream, called “concentrate”, represents a significant disposal challenge. Concentrate treatment to either harmless by-products or complete destruction has so far been costly, from both a capital and operating perspective. Thus, the disposal options for concentrate usually involve transport off-site, shifting responsibility for their ultimate disposal to another environmental system or other approaches. According to the literature surveys conducted for this project, the typical method of brine residuals disposal is discharge to wastewater treatment plants (WWTPs) or to the sea or other water body.
Goals and Objectives
The project provides practical guidance to utilities concerning the effects of membrane process residuals on wastewater treatment (including treatment processes, effluent quality, and water reuse and residuals management options).
Research Approach
The project consisted of four major elements;
- a literature survey,
- an Internet survey to determine water and wastewater utility experience with membrane residuals,
- the development of models to determine the impact of residuals disposal on collection systems and wastewater treatment plants, and
- the development of a guidance manual.
A literature search was conducted to ascertain the impacts of membrane discharges on collection systems and WWTPs followed by a survey of over 250 facilities. Information from the literature survey as well as the survey helped to define two models to ascertain impacts. The first model determines the impact of membrane residual discharges on the collection system. The other model developed is a mass balance model which is a water mass balance including water losses through leaks in the distribution system, water sold outside the wastewater service area, water reuse from both a satellite plant and an effluent reuse facility, and evaporation. A guidance manual was developed to provide utilities with this information.
Findings and Conclusions
This project provides utilities with two types of models for predicting the impacts of membrane concentrate loadings on the collection system and the wastewater treatment plant. Point source impacts reflect the discharge of concentrates to the wastewater collection system and are evaluated with models developed using Excel. These models can project possible deterioration of the collection system at the point of discharge of concentrates to the system. The impacts of system-wide concentrate discharges are evaluated with an Excel mass balance model. Models for discharges to the collection system are provided to calculate the concentrations of components in discharges.
The system-wide mass balance and its features allow almost any water and wastewater treatment system to be modeled. The model is a water mass balance that includes water losses through leaks in the distribution system, water sold outside the wastewater service area, water reuse from both a satellite plant and an effluent reuse facility, and evaporation. The mass balance tracks a number of both conservative and nonconservative pollutants. The conservative pollutants are never destroyed, while the nonconservative pollutants are partially destroyed or converted into another physical form. The report consists of a guidance manual, which compiles all the information developed for this project and a CD-ROM, which includes the Excel models.
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