Pretreatment And Cleaning Lab Report

CHAPTER 6

PRETREATMENT AND CLEANING

Pretreatment and cleaning are two independent processes that could also be related to each other at the same time. Such methods are crucial for seawater reverse osmosis for what they bring from cost and residence time reductions to the increase in the production quality.

6.1. Pretreatment

Various pretreatment methods are used and they include: biofilter, subsurface intake systems, conventional treatment, biological activated carbon, and chlorine injection.

6.1.1. Biofilter

In reverse osmosis, various problems might arise; however, the major problem that could be faced is biofouling, so its reduction would be efficient and beneficial for the process itself; and therefore, it was suggested to treat the
The fixed bed biofilter was developed to remove pathogenic organisms; specifically, Legionella pneumophila, from process water in order to reduce the accumulation on separation membranes that would lead to biofouling. The biofilter was tested in the laboratory first while circulating continuously cooling water system and compared to the results obtained from an identical system but with the absence of the biofilter. The aim of the experiment was surely to find a way to reduce biofouling before its occurrence by improving the quality of the water used. The agent used to create biofouling in the laboratory was organic carbon that is made of the following ingredient; sucrose and yeast, and the results were as follows. The process where the biofilter was used showed a noticeable reduction in the concentration of the fouling organisms; whereas, a high concentration was observed in the absence of the biofilter. The presence of the biofouling agents and the differentiation between both experiments is determined by the heat exchanger. When the biofouling agents got accumulated on the heat exchanger, a large increase in the temperature gradient
Biological activated carbon

Another type of pretreatment for desalination reverse osmosis is the use of Biological Activated Carbon (BAC). This type of pretreatment helps in reducing the biofouling occurring during the desalination processes for its usage later in agriculture knowing that the water that should be used should be moderately saline and is known as “Biologically treated secondary effluent”. After some experiments using the biological activated carbon, it appeared that the pretreatment is useful especially since it proved to dissolve the organic compounds and hinder the growth of biological organisms [4].

Recently, microfiltration and ultrafiltration technologies are commonly being used in the desalination processes for its various advantages; such as, increasing quality of permeate and reliability in operation; however, the major problem occurring in such processes is as discussed previously and known as biofouling. Treatment was first tried with powdered activated carbon that appeared to be able to remove dissolved organic matter but still could not affect the biopolymers that have a high fouling potential, and hence could not affect the flux. Another experiment was performed using a slow sand filter as a pretreatment and followed by ultrafiltration; the flux appeared to have improved since the major foulants were removed; however, the humic substances that are considered important foulants were not majorly affected. The only pretreatment that was majorly