Finance savvy wastewater treatment options

Finance savvy wastewater treatment options 

Numerous industries utilise water in their process towards the production of value added products. More often than not, the byproduct of this production process is a wastewater stream. As part of the enterprise’s water and wastewater management strategy, management needs to decide on the quality of process water required for production operations, if the wastewater generated will be treated to environmental discharge standards or recovered, treated and then recycled back into process operations. 

Once this broad framework has been established, the treatment route of both the process water and wastewater is then considered. High on the list of requirements is the most efficient and cost effective treatment process that results in the lowest operating and capital expenditure. In practice however, the end result will be a trade off between the two i.e., Higher capital and lower operating expenditure vs higher operating and lower capital expenditure.

As part of the planning process, there are a few considerations that can potentially assist in reducing industrial enterprise’s capital and operating expenses. These considerations are discussed below.

Is Reverse Osmosis really necessary?

Reverse Osmosis is an excellent membrane treatment process which can produce water of extreme purity. Because of this, industries tend to overuse Reverse Osmosis and treat it as a “one size fits all” approach, even when it may not be necessary or cost effective.

While Reverse Osmosis can produce a stream of pure water, it requires extreme high pumping pressures which result in higher energy requirements. This equates to higher operating and capital costs for buying electricity and specialised equipment which can handle the extreme operating conditions. In addition, pretreatment techniques depending on the incoming stream may often be necessary in order to reduce fouling and wear and tear of the Reverse Osmosis membranes.

Lastly, the Reverse Osmosis process produces a concentrated waste stream that needs to be discarded, and depending on the type of waste and quantity, may substantially add to the cost of operation.

Other separation techniques should be evaluated first before considering Reverse Osmosis, and if a membrane process is required, then Nano-filtration and Ultra-filtration should be considered first to see if they can get the job done. This may aid in reducing operating and capital costs as less energy, and specialised equipment to handle extreme operating conditions may be required.

Have you considered variable frequency drives?

Most industrial operations require pumps for the transfer of liquids/slurry from one process unit to the next. In general, pumps contribute to the bulk of energy consumption in plants. This is more so the case during start-up and when they pump below the flow rate they have been designed to.

Variable frequency drives aid in reducing the energy consumption of pumps by adjusting the flow/pressure to the required demand at that point in time (this is also the case during start up). The variable frequency drives work by controlling the frequency of the electrical power supplied to the pumps. Pumps with variable frequency drives should definitely be a consideration for any enterprise looking to reduce their energy demand and operating expenses over time.

Have you considered pressure exchangers?

If processes utilising high pressure feed streams such as membrane Nano-Filtration or Reverse Osmosis are included as part of the treatment route, pressure exchangers should be a consideration.

Pressure exchangers work by transferring hydraulic energy from concentrate streams leaving the membranes unit to mechanical energy. The mechanical energy is then used to assist the feed pumps to pressurise the incoming feed stream to the required system pressure. The result is that feed stream pumps draw less energy to create the required pressures for separation through the membrane. Less energy equates to lower electricity costs and thus lower operating costs.

Are heat exchanger networks part of your design philosophy?

Process streams requiring heating and cooling require utilities and energy input to achieve the desired temperature. This energy input may be quite substantial if flow rates are high and target temperatures differ significantly from ambient temperatures.

Heat exchanger networks aid in the energy recovery of both hot and cold streams in order to cool or heat other process streams. I.e a hot output process stream may be used to heat an incoming process stream and a cold output stream may be used to cool an incoming process stream.

This energy recovery and utilisation reduces the number of utilities required in the process which may save capital costs. In addition, less energy is used to cool and heat process streams which in turn reduces electrical costs and thus operating costs.

While not exhaustive, the above suggestions provide a starting point for industrial enterprises to consider for methods towards reducing  project costs.

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