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Testimonials

Water & Wastewater Engineering het hom bewys as 'n maatskappy wat die ekstra tree loop vir sy kliente.
Dean Wasserman (Direkteur Ingenieursdienste)
Die kwaliteit en passie waarmee die maatskappy sake doen is onberispelik en ek kan hulle ten sterkste aanbeveel vir enige konsultasie en ingenieurswerk in die water- en riool suiwerings dissiplines.
Dean Wasserman (Direkteur Ingenieursdienste)
Die professionele wyse waarop u so 'n projek hanteer het word opreg waardeer.
JJ Hoffman (Weskus Distriksmunisipaliteit)

Technologies

Seawater Desalination

Desalination refers to any of several processes whose primary function is to remove dissolved minerals from water. These terms have been generalized in the water industry to mean the reduction of total dissolved solids (TDS) from seawater which has a very high salinity level, typically in the range of 35,000 to 45,000 mg/l. However, these terms would also be applicable to the treatment of any water with a TDS in the high range to make it usable.

Currently, the two practical methods to desalinate seawater are either via a thermal process or a pressure membrane process. The thermal processes utilized are Multi-Stage Flash (MSF), Multi-Effect Distillation (MED) or vapour compression (VC). The pressure membrane process utilized is reverse osmosis (RO). Each of the treatment mechanisms consumes significant power to complete the process. In the thermal processes the power originates in the form of steam while for the membrane process it is electricity. Historically, the thermal process was the only viable technology for desalination but it is now generally accepted that seawater reverse osmosis (SWRO) is the most economical process. Thermal distillation practices can be more economical if the cost of fuel to produce the steam power is significantly lower than the cost of the electric power, thus, limiting thermal desalination primarily to the Middle East.

The heart of the SWRO system is the high pressure membrane that is the molecular sieve that separates the dissolved solids from the water. Pressure, at about 7 000 kPa (70 bar or 1000 psig), is the driving force used in the process. The SWRO system converts approximately 35 60% of the raw seawater to product water (permeate) sometimes making the handling of the wastewater (concentrate or reject) a major concern in the system design.

Large-scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater. In areas where fresh water is limited and/or in areas where municipal water and sewer fees are high, desalination production can be a desirable solution.

MEMRANE BIOREACTORS

The Membrane Bioreactor (MBR) process replaces the secondary settling tank typically used in conventional wastewater treatment for solid/liquid separation. Unlike secondary settling tanks, the final effluent quality is not dependent on the mixed liquor suspended solids concentration or the settling characteristics of the sludge. The MBR systems can operate at much higher mixed liquor suspended solids (MLSS) concentrations than conventional activated sludge systems. This results in a significant smaller footprint for the biological reactor.

A Membrane Operating System (MOS) typically incorporates one or more Membrane Filtration Cells located adjacent to the biological reactor. The biological section of an MBR plant typically includes:

  • Primary waste water treatment, including fine screening and grit removal;
  • A biological treatment system, often including anaerobic, anoxic and aerobic zones;
  • Flow balancing

Following the biological process, the Membrane Operating System (MOS) typically includes:

  • A Mixed Liquor recycle which recirculates Mixed Liquor from the biological reactor through the MOS;
  • One or more Membrane Filtration Cells. Each Cell is a tank in which several Racks are fitted. Each Rack holds a number of Membrane Filtration Modules and has manifolds to collect filtrate and distribute low pressure air. Cells may be covered for odour control;
  • An aeration system which continuously supplies low pressure air to the Filtration Modules in each Cell;
  • A Filtrate Pump, which draws filtered liquid from the Membrane Filtration Modules in the Cell;
  • Valves, instrumentation and controls [including programmable logic controller (PLC) and human machine interface (HMI)];
  • Ancillary equipment, such as a compressed air system and chemical storage/delivery system, to provide operating and cleaning resources;
  • Downstream storage and processing systems (such as disinfection or Reverse Osmosis);
  • Maintenance components, such as a Rack Removal System and special tools.

DAF

Dissolved air flotation (DAF) is a water treatment process that clarifies water by removing suspended matter such as oil or solids. The removal is achieved by dissolving air in the water under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.

Dissolved air flotation is very widely used in treating the industrial wastewater effluents from oil refineries, petrochemical plants, natural gas processing plants and similar industrial facilities.

Ozone

Ozone treatment of drinking water benefits water quality in several ways. It prevents formation of trihalomethanes and other organochlorine compounds by decomposing humic acids.

Ozone deodorizes drinking water by breaking down two major compounds that contribute to musty smell i.e. geosmine and 2-methylisoborneol, which most other processes do not remove. Combined with activated carbon filtration, it serves to remove agricultural chemicals, wastes from high-tech industrial processes and other substances listed in water-quality regulations.

Powder Activated Carbon

Adsorption is a physical process where soluble molecules (adsorbate) are removed by attachment to the surface of a solid substrate (absorbent) primarily by van der Waals forces, although chemical or electrical attraction may also be important. Adsorbents must have a very high specific surface area and include activated alumina, clay colloids, hydroxides and adsorbent resins, with the most widely used being activated carbon. To be effective the surface of the adsorbent must be largely free of adsorbed material, which may require the adsorbent to be activated before use (McKay, 1996). A wide range of organic materials are amenable to removal by adsorption, including detergents. In water treatment it is used to remove taste and odour as well as colour and other organic residuals, especially chlorination disinfection by-products such as THMs.

The most widely used adsorbent is activated carbon which can be produced by pyrolytic carbonization using a number of different raw materials including bituminous coal, lignite, peat and wood. Particles are irregular in shape with a highly porous internal structure providing the large available surface area for adsorption. The rough external surface is ideal for the attachment of micro-organisms which can enhance adsorption by biological removal mechanisms.

Powder activated carbon (PAC) offers unique design flexibility. It can be added to the water at various stages within the water treatment processes. It can also be used on an intermittent basis which is particularly useful in controlling seasonal taste and odour problems in drinking water caused by algae, actinomycetes or fungi. In water treatment PAC is fed directly into the water stream as a slurry either at the rapid mix stage of chemical coagulation or immediately prior to sand filtration. As the PAC must be removed from the treated water its addition at the coagulation stage ensures maximum contact time and mixing to occur, with removal of the PAC by sediment and sand filtration.

Granular Activated Carbon

Granulated activated carbon (GAC) has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Granulated carbons are used for water treatment mostly for deodorisation and polishing of water. GAC can be either in the granular form or extruded.

Biological Activated Carbon

Biological activated carbon (BAC) filtration is a drinking water treatment process widely applied. BAC removes organic carbon components like pesticides, THM-precursors, colour, taste and odour compounds by the combinations of absorption and biodegradation.

Filters

The rapid gravity sand filter is a type of filter system that is used in the purification of water and is commonly used in municipal water treatment facilities.

Rapid gravity sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals - typically salts of Aluminum or Iron. Water and flocculants flows through the filter medium under gravity and the flocculated material are trapped in the sand matrix.

Rapid gravity sand filters must be cleaned frequently, often several times a day, by backwashing, which involves reversing the direction of the water. During backwashing, the bed is fluidized and care must be taken not to wash away the media.

Rapid gravity sand filtration has very little effect on taste and smell unless activated carbon is included in the filter medium.

List of other treatment technologies:

  • Anaerobic digestion
  • Activated sludge
  • Trickling filters (Bio-filters)
  • Batch reactors
  • Ultra filtration
  • Ultraviolet/Peroxide disinfection
  • Wetlands
  • Composting