CHAPTER 4 CASE STUDIES
4.3 COMPANY B
The company is a job shop situated in Jacobs, Durban, South Africa. At the time of the study, the company was 15 years old and had 10 employees. Galvanising and powder coating of metal objects was provided as a service for various customers. The objects to be plated were mainly burglar guards and large gates
4.3.1 Process Description
The main processes employed at the company were zinc plating and powder coating. White, black, and brown powder coating was carried out with approximately 90 % of the white powder being recovered and reused.
The investigation focused on the main zinc line since its consumption of water and chemicals and the generation of effluent were of concern to the company. The process flow diagram is illustrated in Figure 4.4. Overflow rinses are indicated by the dashed lines.
~
Zinc
---+ Degrease --+ Rinse ~ Pickling --+ Rinse --+ Plate --+ Rinse r--
.,
....... Effluent Treatment~
PassivateH
RinseH
Hot RinseI
Figure 4.4: Process diagram of zinc plating process
The plating process was completely manual. Rinsing of small jobs was carried out in static rinses, while the larger articles were rinsed off with a hosepipe. Some barrel plating took place, but the larger jobs (burglar guards and gates) were immersed into the baths by workers.
4.3.2 Water Consumption
The company used municipal water. Water was used mainly for rinsing purposes. The company had one water meter, which was read daily. Records of water consumption were kept, but the company was charged for its water use by the landlord and thus did not receive a separate water bill.
4.3.3 Chemical Consumption
The jobs were degreased in a caustic cleaning solution, while hydrochloric acid was used for pickling. Other major chemicals used include sodium cyanide, sodium hydroxide and passivates.
The company was not able to provide details of chemical use.
4.3.4 Energy Consumption
Energy was used mainly for the drying ovens following the powder coating process and the heating of process baths.
4.3.5 Wastes Generated
The main areas investigated were air emissions and effluent.
Air Emissions
The cyanide zinc process was the main source of air pollution. Some evaporation occurred from the degrease and acid tanks.
Effluent
Rinsing operations contributed the largest proportion of the effluent stream. Spills and floorwash drained into the effluent holding tanks. Regular dumping of the acid and alkali baths took place.
Effluent treatment was carried out in three tanks installed in the ground. Cyanide was treated by the addition of sodium hypochlorite, and the pH was controlled with soda ash.
4.3.6 Waste Minimisation Programme
The company was a member of the waste minimisation club since its inception, and its management signed a declaration of commitment to waste minimisation. Complying with new regulations and learning more about waste minimisation were the primary reasons for the company joining the club.
The company had two project champions, the owner and the manager. They were responsible for co-ordinating waste minimisation activities at the factory, and ensured that the workers were aware of the efforts being made and the importance of these efforts.
Problems Identified
During the assessment the areas chosen for investigation were:
• water consumption,
• chemical consumption,
• metals lost to drain, and
• effluent treatment and control.
While the company kept records of its water consumption, this was not used to monitor its use or to compare it with the amount for which the company is charged. No control was being exercised over the amount of water used for rinsing jobs by hosepipe. Odd shaped containers were used as static rinse baths for small jobs. The process baths were not arranged for the optimisation of
the process with respect to space and time. As a result, workers had to carry jobs around leading to drainage over the floor. This resulted in a loss in water, chemicals, and metals.
Further losses were incurred by insufficient drainage of jobs and dragout. The company did not have a proper effluent treatment plant.
Waste Minimsation Options
The investigation lead to a total of 19 waste minimisation options being identified for the site. The company was very keen to implement the options and improve conditions on site, and had implemented eight options by November 2000. Savings in water and chemicals were realised.
• Water Consumption:
The company began monitoring water consumption so that discrepancies could be identified. A reduction of water use was achieved through the fixing of leaks in pipes and tanks. A maintenance programme made possible the quick detection and repairing of further leaks.
Efforts were made to train shop floor employees on the importance of saving water. These measures led to a saving in water of 220 kL/year.
• Chemicals and Metals
Drip trays were installed to collect spills and reduce dragout. The solution collected was used to top up process baths. An overhead drainage bar was installed for the zinc tank to increase the drainage time of larger jobs. More control was exercised over the use of chemicals, and the company undertook to conduct its own analyses of process baths to prevent excess addition of chemicals. These changes resulted in savings in process chemicals, zinc metal, and treatment chemicals. Cyanide consumption in particular has been decreased by 40 kg/month.
• Effluent Treatment and Control
The reduction in water use and chemicals and metals lost to drain resulted in a lower volume of effluent requiring treatment and therefore lower treatment costs. The company was also building an effluent treatment plant to enable compliance with bylaws.
4.3.7 Economic Benefits
The company benefited from savings in water and chemicals. The savings achieved as· at November 2000 are shown in table 4.3.
Table 4.3: Savings Achieved Item
Water
Chemicals and Metals Total
Annual Saving (R/yr) 636
13 200 13836
Pay-back Not quantified Inunediate
4.3.8 Environmental Benefits
The company's environmental impact was reduced by the implementation of waste minimisation.
Savings to the environment as at November 2000 include:
• a reduction in water consumption by 220kL/year,
• a reduction in cyanide use by 4 800 kg/year,
• a reduction in metals to drain, and
• a reduction in volume of effluent discharged.