WATER & WASTE TREATMENT INDUSTRY FOCUS A MODERN APPROACH TO BRINE DISPOSAL


Peter Nicoll, technical director at Modern Water, explains how the company’s membrane-based brine concentrator is proving successful in water treatment. While Soham Mehta, managing director at Advent Envirocare Technology, praises the pilot trials


W


hether it be from a process or from Reverse Osmosis (RO)-based


recycling or desalination, the challenge of waste brine disposal usually requires costly thermal treatment, leading to Zero Liquid Discharge (ZLD). However, a technological breakthrough looks set to change all this. A new, non-thermal system that simply


uses electrical energy and consumes only a fraction of the energy compared to thermal systems is now available. Following its first full-scale demonstration plant, built and operated in India, this pioneering work (developed from Modern Water’s knowledge of forward osmosis and osmotically-driven membrane processes), feels and operates just like standard RO systems, and doesn’t require specific expertise to operate it. Typically, expensive Seawater Reverse


Osmosis systems have been deployed to concentrate brines to about 7-9% NaCl equivalent, but these are limited by the hydraulic pressure that membranes can withstand. More recently, some Plate & Frame and Disc-type RO configurations have been developed. These can withstand much higher pressures than traditional spiral-wound Seawater RO membranes, but challenges still remain in overall system design and sourcing of system components at such high operating pressures, which limits their applications. Peter Nicoll, technical director at


Modern Water, commented: “There is no such generalisation of the word ‘brine’ in the wastewater industry and it covers the entire spectrum of salinity from cooling tower blow-downs to saturated solutions from production processes in the chemical industries. In the Indian market, what is common though to both water and wastewaters is that the effluent disposal standards do not permit any waters higher than 2100 mg/l of Total Dissolved Solids (TDS) to be discharged into surface waters or the land. Disposal of brine is a serious environmental issue, attracting more and more focus from the authorities – and the courts.” Nicoll also explained that with proper


pre-treatment (and intermediate treatments for removal of sparingly soluble salts, heavy metals and organics), traditional seawater RO membranes are often used to concentrate wastewater brines to about 50-70,000 mg/l (5-7%) NaCl equivalent concentration, though


/ PROCESS&CONTROL


theoretical possibility is somewhat higher at 9%. To adhere to discharge laws, industries rely on thermal treatments like Multiple Effect Thermo-Compressor Evaporators or Mechanical Vapour Compressor (MVC) Evaporators. These distil out the water from the concentrated brine, thereby yielding wet salt, which is then disposed to a secured landfill. Since Thermal Brine Concentrators are


costly and also difficult to operate continuously and reliably, effort has gone


The membrane-based brine concentration technology has evolved out of the Forward Osmosis - Reverse Osmosis-based seawater desalination technology, invented and patented by Modern Water


Graph showing different brine concentration technology


in to finding more efficient solutions. From solar pans to salinity gradient solar ponds, solar stills to psychometric evaporators, or Membrane Distillation to Capacitive Deionisation, major investment has been made to concentrate brine from the RO step, but with limited success. This membrane-based brine


concentration technology has evolved out of the Forward Osmosis - Reverse Osmosis-based seawater desalination technology, invented and patented by Modern Water. Forward Osmosis, or simply Osmosis, is nature’s way of attaining osmotic equilibrium when two fluids of different osmotic pressure, or different concentrations of dissolved constituents, are separated using a semi- permeable membrane. Osmosis was first scientifically recorded in 1748, while Reverse Osmosis was invented in the 1950s. Forward Osmosis, on the other hand, has only seen commercial applications in the past decade, and is characterised by employing a specific draw solution or osmotic agent to extract water from the feed. The first prototype of the membrane-


based brine concentrator was built in India and tested successfully in late 2016/early 2017 at Ahmedabad. Soham Mehta, managing director of


specialised environmental engineers, Advent Envirocare Technology Pvt, said: “Subsequent to the successful proof-test, the system was shipped to a major dyestuff manufacturer for a pilot test on brine generated from a dye-desalting Nanofiltration system. The trials were very successful, with a feed TDS of 4-5% being concentrated to 13.5%, thereby yielding 67% average recovery. The image below shows the feed, brine and permeate samples from the plant during the large- scale pilot testing.” Pilot trials are also underway with an agrochemical waste brine having 6-7% TDS, mainly sodium sulphate, with a target concentration of concentrated brine as 16%. The new Membrane Brine Concentrator


from Modern Water can even be deployed at seawater desalination facilities to produce more water from the reject brine, or for treating mining effluents and FGD system bleeds – addressing industry’s dire need for a cost-effective solution to challenging brine concentrations. A full-length version of this article is


available by contacting Modern Water using the details below.


Modern Water T: 01483 696000 E: info@modernwater.co.uk www.modernwater.com


PROCESS & CONTROL | SEPTEMBER 2018 31


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