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The Assessment of Rietspruit Wastewater Treatment Plant Essay

The plant currently does not comply with the DWA wastewater discharge standards. There are major challenges with respect to operation, maintenance and some equipment status at the plants. Some of the problems identified that are hampering the non-compliance of the final effluents are as follows: •Flow meters are not calibrated (incorrect flow readings) and this makes it difficult to optimize the plant with respect to flows into different modules, i.e. Activated Sludge plant and the trickling filter plant.” •Over aeration (due to the oversized aerator blades) taking place in the extended aeration basin causing excessive foaming in the biological reactor and final settling tank. •The internal Recycle Pumps in the aeration are not Variable Speed Drives (VSD) as a results incomplete treatment is taking place in the reactor and a high current is pulled by these pumps.”

• The suction lift clarifier scum box not working resulting in the excess scum formation on the clarifier and non-compliant of effluent being discharged into the river. Two of the suction lift valves (siphons) kept on blocking due to the high sludge concentration in the clarifier resulting in sludge carry-over to the river.” •Three bio-filter are non-operational due to the defective central columns and structures. •All six sludge digesters are full of grit and sand thereby reducing the working volume of the digesters and the efficiency of the sludge treatment. Some of the valves at the digesters are old and defective making it difficult to operate the digesters at full capacity.

•Some of the sludge drying beds are defect and need urgent repair for sludge handling purposes. •There are not enough process control instruments for plant optimization and control; instruments such as Dissolved Oxygen Meter, pH Meter (for sludge digestion), Ammonia and phosphate kits. •The plant does not have a proper chlorine contact chamber for effective disinfection of the final effluent. •There are currently not enough classed operators at the plant.

Short term Solutions

1.Process Improvement

The inlet works flow meters need to be calibrated or replaced in order to gauge the flow into different modules and process optimization. The internal
recycle pumps must be converted to VSD for the effective nutrients removal in the reactor. The aerator blades in the reactor must be adjusted/replaced with correct size to prevent over aeration from taking place and unnecessary power consumption. The scum box in the final clarifier must be repaired to prevent excessive formation of scum layer on the clarifier. The clarifier must be decommissioned (for one day) and water pump out to a point where accessibility and repair work can be done.

All the flows to be diverted to the bio-filters during the repairs of the scum box and modification (if need be). Central columns of the defective bio-filters to be repaired/ replaced to ease the hydraulic load on the activated plant. Process control instruments to be made available/purchased (by Rand Water) for effective plant control and optimization. Chlorine contact chamber must be constructed for the effective disinfection of the final effluent. All six sludge digesters must be cleaned out. Damaged pipes and valves must be repaired for effective sludge handling at the plant. All damaged sludge drying beds must be repaired.

2.Maintenance

A scheduled preventative maintenance for mechanical, electrical and instrumentation to implemented for the effective operation of the plant and extension of equipment life. All defective mechanical, electrical and instrumentation equipment to be repaired by Rand Water maintenance personnel for plant availability at all times.

3.Human Resource

There are currently not enough classed operators at the plant. This is having a negative impact on the operation of the plant. Recruitment of unemployed science graduates from the Emfuleni Local Municipality to be trained and paid by Rand Water for a period of a year. Additional six (6) general workers to assist with estate maintenance, unblocking of bio-filters, reactors and clarifier cleaning will ease the work load on operator on duty.

Long term solution

For Riestpruit WWCW to be 100% compliant with discharged standards of final effluent, the effluent from the humus tank of the bio-filters must be further treated in the activated sludge plant for removal of nitrates and phosphates. This can be achieved by pumping the effluent from the humus tank/bio-filters into the anoxic zone of the activated sludge plant. This will eventually lead into the construction of the second clarifier to ease the solids and hydraulic load on the first clarifier. This recommendation is made on light that even after the Regional Scheme is in full operation, Rietspruit WWCW will be operational for at least 12 – 15 years.

Assessment Report – Rietspruit WWTW27-09-2009

The plant currently does not comply with the DWA wastewater discharge standards. There are major challenges with respect to operation, maintenance and some equipment status at the plants. Some of the problems identified that are hampering the non-compliance of the final effluents are as follows: •Flow meters are not calibrated (incorrect flow readings) and this makes it difficult to optimize the plant with respect to flows into different modules, i.e. Activated Sludge plant and the trickling filter plant.” •Over aeration (due to the oversized aerator blades) taking place in the extended aeration basin causing excessive foaming in the biological reactor and final settling tank.

•The internal Recycle Pumps in the aeration are not Variable Speed Drives (VSD) as a results incomplete treatment is taking place in the reactor and a high current is pulled by these pumps.” • The suction lift clarifier scum box not working resulting in the excess scum formation on the clarifier and non-compliant of effluent being discharged into the river. Two of the suction lift valves (siphons) kept on blocking due to the high sludge concentration in the clarifier resulting in sludge carry-over to the river.” •Three bio-filter are non-operational due to the defective central columns and structures. •All six sludge digesters are full of grit and sand thereby reducing the working volume of the digesters and the efficiency of the sludge treatment. Some of the valves at the digesters are old and defective making it difficult to operate the digesters at full capacity.

•Some of the sludge drying beds are defect and need urgent repair for sludge handling purposes. •There are not enough process control instruments for plant optimization and control; instruments such as Dissolved Oxygen Meter, pH Meter (for sludge digestion), Ammonia and phosphate kits. •The plant does not have a proper chlorine contact chamber for effective disinfection of the final effluent. •There are currently not enough classed operators at the plant.

Short term Solutions
1.Process Improvement

The inlet works flow meters need to be calibrated or replaced in order to gauge the flow into different modules and process optimization. The internal recycle pumps must be converted to VSD for the effective nutrients removal in the reactor. The aerator blades in the reactor must be adjusted/replaced with correct size to prevent over aeration from taking place and unnecessary power consumption. The scum box in the final clarifier must be repaired to prevent excessive formation of scum layer on the clarifier. The clarifier must be decommissioned (for one day) and water pump out to a point where accessibility and repair work can be done.

All the flows to be diverted to the bio-filters during the repairs of the scum box and modification (if need be). Central columns of the defective bio-filters to be repaired/ replaced to ease the hydraulic load on the activated plant. Process control instruments to be made available/purchased (by Rand Water) for effective plant control and optimization. Chlorine contact chamber must be constructed for the effective disinfection of the final effluent. All six sludge digesters must be cleaned out. Damaged pipes and valves must be repaired for effective sludge handling at the plant. All damaged sludge drying beds must be repaired.

2.Maintenance

A scheduled preventative maintenance for mechanical, electrical and instrumentation to implemented for the effective operation of the plant and extension of equipment life. All defective mechanical, electrical and instrumentation equipment to be repaired by Rand Water maintenance personnel for plant availability at all times.

3.Human Resource

There are currently not enough classed operators at the plant. This is having a negative impact on the operation of the plant. Recruitment of unemployed science graduates from the Emfuleni Local Municipality to be trained and paid by Rand Water for a period of a year. Additional six (6) general workers to assist with estate maintenance, unblocking of bio-filters, reactors and clarifier cleaning will ease the work load on operator on duty.

Long term solution

For Riestpruit WWCW to be 100% compliant with discharged standards of final effluent, the effluent from the humus tank of the bio-filters must be further treated in the activated sludge plant for removal of nitrates and phosphates. This can be achieved by pumping the effluent from the humus tank/bio-filters into the anoxic zone of the activated sludge plant. This will eventually lead into the construction of the second clarifier to ease the solids and hydraulic load on the first clarifier. This recommendation is made on light that even after the Regional Scheme is in full operation, Rietspruit WWCW will be operational for at least 12 – 15 years.


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