CASE STUDY

Frozen Food Processing Facility - South Africa

Problem to be solved:

Production of an effluent with high suspended solids content, intermittent COD non-compliance and a low pH. Discharge of the water may lead to fines if left untreated as well as load the downstream constrained municipal wastewater treatment infrastructure.
  • How we solved it:
  • Benefits to Client’s business:

CWC installed a pH dosing system and steel lamella clarifier to remove solid food waste from the water.
Caustic dosing was use to elevate the pH to 6.5. Dosing was controlled through the use of a pH sensor and caustic was delivered by duty standby dosing pumps.

The flocculation system comprised a cationic powdered flocculent with educator system and hydration tank. Once mature, the flocculent was dosed upfront of the clarifier by duty standby dosing pumps.

The dosing system included liquid coagulation dosing, also by duty standby dosing pumps.

The lamella settler is responsible for allowing solids to settle and clear water to decant from the system. Cleat water was released to drain while sludge underflow from the settler was pumped to a decanter to be dewatered.

Minimising environmental impact and the additional loading on a constrained receiving municipal wastewater treatment plant as well as limiting risk on potential non compliance fines.

CASE STUDY

Gold mine - Guinea

Problem to be solved:

Gold mine required 30 m3/h low TDS water for their operations. Feed water was unsuitable for direct use and required treatment.
  • How we solved it:
  • Benefits to Client’s business:

The containerized packaged plant consists of a reverse osmosis (RO) system with pre-treatment producing 30 m3/h low conductivity water (<15 TDS). The system is designed to receive raw water with a total dissolved solids (TDS) content of 951 ppm.

The pre-treatment consists of a duty/standby pump feed system that pumps water through a multimedia, activated carbon and bag filters. The multimedia collects suspended solids from the feed water as the raw water passes from top to bottom. Most important for the multimedia filter is that this solids in the media bed is removed during the backwash steps. A backwash step consists of two steps of which the first is the reverse flow through the media bed where water enters at the bottom of the vessel and exits at the top where it is discharged to waste. This step is directly followed by the rinse step that resettles the filtration bed by flow going from top to bottom and exiting to waste.

The next vessel after the multimedia filter is the activated carbon (AC) filter. The purpose of activated carbon is to remove odors and organics from the feed water. It to some degree also removes free chlorine which damages the RO membranes. The AC filter operates in the same way as the MM filter with flow going from top down during service. The AC filter will go through a backwash on a regular basis. The factory set settings are a single backwash once a day. But this can be increased should the solids loading be higher in the feed water.

Before the MM filter sodium hypochlorite is dosed as a disinfectant. This will keep the MM filter and AC filter disinfected. It should however be noted that free chlorine damages the RO membrane irreversibly. For this reason, sodium metabisulfite is dosed before the RO to remove possible residual free chlorine. Free chlorine will also be removed from the system when water is passed through the AC filter.

As a last polishing step before water is discharged into the break tank the MM product water is passed through a bag filter system. Product water after the bag filters is discharged into a break tank with high level so that the pumps stop running when break tank level is high. From the break tank water is drawn into the RO section which is the second section.

The reverse osmosis plant draws water from the break tank with centrifugal low-pressure pump. The passes through two high flow filters. The cartridge filters prevent any solids passing to the RO membranes where it will cause fouling of the membranes. The filtration sizes of the cartridges are 20 µm and 5 µm in respectively. Before water enters the high pressure pump there are two dosing points which is for anti-scalant and SMBS respectively. Anti-scalant is dosed to inhibit the formation of scale on the membrane surface. It is critical that this chemical is dosed to prevent non-reversible scaling. The second chemical is dosed to remove remaining free chlorine in the feedwater.

Water is fed to the RO membranes at high pressure (approx. 10.6 bar) with the high pressure pump that would feed two trains with a two stage RO configuration. A low pressure switch protects the pump in case of no flow/pressure. The two first stage trains consist of 2 membrane vessels of 6 membranes each while the second stage is one membrane vessel with 6 membranes. The RO runs with a feed flow of 40 m3/h at a 75% recovery rate. This means that the total reject flow rate is 10 m3/h. Product is discharged to product tank.

The RO also has a cleaning in place (CIP) system which is also used for flushing. Flushing will occur when the plant has been stagnant for a pro-longed period i.e. 30 minutes. This typically happen in the case of a low feed tank or full product tank. The reason this is done is to remove concentrate that are sitting on the membranes from operation by flushing it with clean water in flush tank. The CIP/Flushing tank is therefore filled with permeate during the start of operation. A CIP should be done at least every three months or in the cases stipulated in this manual.

Ensuring they have sufficient water of the correct quality for their mining and processing operations.

CASE STUDY

Property developer - South Africa

Problem to be solved:

Property developers required a 10 m3/h disinfection plant to render feed water safe for drinking.
  • How we solved it:
  • Benefits to Client’s business:
The feed water will be dosed with sodium hypochlorite. This will oxidize heavy metals and disinfect the water. The chemically enhanced water will thereafter pass through triple stage filters. The filters are rated 10micron, activated carbon and 1 micron. The micron filters will remove suspended solids and the activated carbon filter will remove organics. The filtered product will then pass through a UV sterilizer which will disinfect the water further. The outlet from the UV will be sent to point of use.

The client was able to provide disinfected, safe water for domestic use.

CASE STUDY

Religious institute - South Africa

Problem to be solved:

The community required treatment of 60 m3/d of borehole water for domestic purposes. The water was high in turbidity, nitrates and bacterial contamination. They system had to be built into and fully interfaced with existing infrastructure.
  • How we solved it:
  • Benefits to Client’s business:

Borehole water was filtered through AFM filters with automatic backwashing heads. The activated filter media ensures that biological contamination of the filter does not take place and provides superior filtration performance when compared to alternative media.
After the water is filtered, it passes through a nitrate column for nitrate removal to reduce nitrate levels in line with SANS 241. The nitrate column is regenerated automatically with a brine solution.

Ozone is used for pre and pots treatment disinfection to remove bacterial contamination it the water and making it safe to drink.

The system is supplied complete with a fully automated control system and requires minimal operator input.

Client was able to provide safe drinking water to their entire community.

CASE STUDY

Copper mine - Democratic Republic of Congo

Problem to be solved:

Mine required borehole water treatment for domestic use. The following parameters are assumed to be outside of the drinking water standard (SANS 241), Suspended solids / Turbidity, Calcium and Magnesium
  • How we solved it:
  • Benefits to Client’s business:

Pre-Disinfection:

10g/h Ozone generator with air pump, stone diffuser and air dryer filter.

Raw water holding tank:

A 2500L LDPE plastic tank has been included for the collection and storage of the raw water. The holding

capacity will ensure enough contact time for the water to be disinfected (~90 minutes).

Pre-treatment (filtration):

  • Duty feed pump to feed the filtration train, complete with suction and discharge isolation valves, discharge check
  • valve and discharge pressure gauge.
  • AFM filter for suspended solids removal complete with automatic valve head for duty and backwash flow.
  • The filter vessel is backwashed using feed water, at a frequency of once per day (or as determined during commissioning).

Reverse Osmosis Skid:

  • The RO skid will be fed from the product from the AFM filter will boost the water through cartridge filters and then into the high pressure (HP) pump. 
  • Antiscalant is dosed into the suction side of the HP pump;
  • Chemical holding tank with bund, 100L, for storage of liquid antiscalant.
  • Dedicated dosing pump, manually set.
  • Integrated level switch to alert the operator to low chemical tank level.
  • Injection nozzle with non-return valve.
  • The skid includes a cartridge filter for protection of the membranes from any carryover particulate, which is complete with pressure gauges on the inlet and outlet for differential pressure monitoring.
  • The RO skid includes four (4) 4040 membranes.
  • The brine line from the RO vessels is split between waste and recycle, each manually set to achieve the desired recycle rate and overall recovery. This brine is combined with the filtration train waste line and totalized using the same flow transmitter.
  • The product water passes through a remineralisation column, to increase the LSI of the water, for protection of downstream steel and/or concrete piping.
  • The product water leaving the RO is dosed with liquid sodium hypochlorite (NaOCl) at a concentration of 5% for final disinfection;
  • Dedicated dosing pump, automatically regulated according to the downstream, integrated ORP reading.
  • Integrated level switch to alert the operator to low chemical tank level.
  • Injection nozzle with non-return valve.
  • It is expected that a 1.5ppm dosage will be applied, which equates to a dosing rate of 0.03L/h.
  • The permeate water is monitored for electrical conductivity and a flow transmitter is installed in the line for monitoring and totalising of the product produced.

The client was able to provide safe drinking water to their employees.

CASE STUDY

Switchgear Manufacturer - South Africa

Problem to be solved:

The client was using costly and hazardous solvents to clean machined parts if switchgear production. They were looking for an alternative, safer system to wash components.
  • How we solved it:
  • Benefits to Client’s business:
BWT Africa installed a softener on their municipal feed to remove calcium and magnesium from the water. Softened water is passed through an RO, prior to polishing with a mixed bed resin to produce Type 1 ultrapure water.
The client was able to the high purity water for component washing and stopped the use of toxic and expensive chemicals in the production process.

CASE STUDY

Meat Processing Facility - Botswana

Problem to be solved:

The water source available to the client had a hardness in excess of 300 mg/L. The water is used in meat processing and the hardness affected both the quality of the end product, as well as the waer circuit infrastructure.

  • How we solved it:
  • Benefits to Client’s business:
BWT Africa installed a duplex softening system, large enough to meet the client’s production needs.
Scaling up of the water system was eliminated and the final meat product didn’t contain high levels of calcium and magnesium.