Chemical Technology April 2015

WASTE MANAGEMENT

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After consultation with the power station staff it was determined that the cooling water clarifier had been over- dosed with flocculant and that the water returning to the tower basin had then flocculated in the basin of the cooling tower. This sludge had settled to approximately 1 m thick in the basin and was contaminating the entire south side cooling water system. The sludge increased the organics in the entire system and the treatment chemicals could not control the microbiological growth. The treatment chemicals’ supplier was contacted and the dosage concentration increased. The basin was dredged on- line due to limitations in taking the tower off-line. The sludge that was removed had turned septic and a full inspection of the cooling tower basin will be undertaken on the next outage to ensure that there is no damage to the concrete. Conclusions The BOMM device offers a simple means of obtaining representative sessile samples from Eskom cooling water systems. The results generated in terms of counts and corrosion rates offers direction to the chemical suppliers on the effectiveness of their regimes. The Microbiology department is in the process of compiling a report which offers the photograph, the bacterial counts and the corro- sion rates for the two metals. References A list of references for this article is available from the editor at chemtech@crown.co.za z

Figure 1: Block one of the BOMM indicating the positions of the corrosion coupons (red).

Figure 2: Block 2 of the BOMM indicating the positions of the corrosion coupons and the rope attachment joints.

Figure 3: BOMM complete indicating the nylon insets (yellow) on the outsides of the blocks

Figure 4: BOMM showing severe fouling and scaling.

Figure 5: BOMM showing biofilm formation and MIC nodule formation on the corrosion coupons.

Figure 6: Algal fouling of the south cooling water system.

Figure 7: BOMM device from the north cooling tower basin.

Figure 8: BOMM device from the south cooling tower basin.

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Chemical Technology • April 2015