Sludge chlorination control

The chemical vendor will supply a biocide additive. The refinery will be responsible for adding chlorine. Controlled addition of biocide and chlorine will limit biological growth and prevent the buildup of slime in the exchanger tubes. Be careful to avoid excessive use of biocide. In one refinery biocide killed the "bugs" in the activated sludge section and was therefore responsible for a major upset at the effluent treating plant. 

M. K. Stenstrom, Optimization of chlorination of activated sludge plant effluent by ammonia control. Technical paper presented at the 1980 Joint Automatic Control Conference, San Francisco, CA. August 13-15, 1980. 

The most common use of chlorine in sewage treatment is for disinfection, which usually is the last treatment step in a secondary biological wastewater treatment plant. Where the treated secondary effluent is fed into a stream to be used for water supply or for recreational purposes, chlorination is effective in destroying the disease-producing pathogens found in treated wastewater. Other principal uses of chlorine are odor control and control of bulking in activated sludge. 

The combined flow is then pumped through the first reaction tank where it is thoroughly mixed. A portion of the sludge then flows to the second reaction tank while the remainder is recirculated. Recirculation of a portion of the sludge aids in mixing and provides better utilization of the chlorine. The recirculation rate is normally held constant. A pressure control pump at the discharge end of the second reaction tank maintains a pressure of 30 0 psi on the entire system. 

The following are the pre-startup procedures (a) Check operation of the chlorine pressure reducing valve (PRV) by turning ON the power switch on the sludge oxidation unit control panel. Turn the chlorine valve switch to the OPEN position, observe operation of valve actuator (b) turn switch to the CLOSED position and (c) adjust time delay relays according to the manufacturer s instruction manual. 

The findings in the crop plants examined for chlorinated hydrocarbons do not reveal any transfer of PCBs from the soil to the crops when the values from the controls and after application of sewage sludge are compared. The increases in content in the soil were not accompanied by any in the crop plants. Nor was there any difference due to the species of crops. At the same time the absolute values indicated very low contents that varied around the figure of 0,001 mg/kg fresh matter. In many cases, there was no positive finding at all where there was absence of evidence (Table 2). 

Lurker PA, Clark CS, Elia VJ. 1982. Atmospherie release of chlorinated organic compounds from the activated sludge process. J Water Pollut Control Fed 54 1566-1573. 

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