The Role of Filtration in Water Conservation

A series of DrM filters in operation

Water has become a scarce resource in many parts of the world. Once abundantly available, supply is running low and demand both for private and industrial use has constantly increased over time. While nations have historically not given too much attention to the conservation of this valuable resource, today nations find themselves increasingly fighting for a larger share of what is at their disposal. In certain regions of China for example, the maximum amount of water usage is specified in licenses for new production plants. Since the size of the plant is defined by its water usage, process technologies, which consume the least amount of water will therefore allow for the largest plant to be built under the terms of a given license agreement.

Water conservation is more important than ever in decision-making. International process licensors and engineering companies are finding themselves adapting their designs to local water usage regulations. Solid/liquid separators play an important role in these processes. They can generally be categorized as follows:

  • Feed water treatment
  • Water conservation and reuse
  • Product recycling from waste water streams
  • Process water recovery

As production plants usually have life cycles of a few decades, they often find themselves confined by older process technologies despite periodic equipment upgrades and revamping. The following sections describe a number of cases in which filtration technology has had a major impact in the above-mentioned categories.

Feed water treatment

Sea water pretreatment prior to reverse osmosis desalination

In coastal areas where seawater is readily available but potable or even utility water is a precious resource (e.g., the Middle East), desalination by means of RO is a very common approach.

Since RO membranes are susceptible to even low concentrations of suspended solids, pretreatment is required to protect them from fouling or contamination, to extend their life and to minimize maintenance downtime. Special mention is needed for algae removal, one of the most challenging pretreatment tasks. Algae growth can proliferate unpredictably depending on seawater temperature. Their colloidal behavior represents a serious challenge for filtration systems.

Conventional pretreatment may include flocculent dosing, multi-media (gravel-sand-anthracite) filtration, cross flow filtration, just to name a few. A solid-liquid separator such as DrM’s FUNDABAC┬« candle filter (also known as a tubular pressure filter) can replace a complete treatment system capable of removing virtually all suspended matter to sub-micron levels.

DrM filters operating with filter aid can successfully remove algae and other suspended solids present in seawater. The filtered water is ideally suited to be processed by RO plants.

Detailed view of DrM candle element design

Detailed view of DrM candle element design

Conservation and reuse of water

Pre-leach and Post-leach operations in TiO2 production

Produced water filtration

Produced water handling filters are installed downstream of a slug catcher or flash drum. During normal operation, the water from the flash drum is processed. Other process streams are intermittently treated, such as wash or pigging water.

Metal sulphates, FeS, free mercury and sand are among the solids to be removed. The amount of solids generated by the system and their tendency to foul increases dramatically during intermittent operations like pipeline pigging. DrM filters can easily adapt to a very wide range of operating conditions as a result of their ability to use filter aid in cases of limited liquid filterability. With its fully enclosed design, the FUNDABAC filter easily fulfills HSE requirements when dealing with hazardous substances (Hg, H2S, NORMs) typically present in well water.

Product recycling from wastewater streams

Recovery of ABS (Acrylonitrile-Butadiene-Styrene copolymer) from a waste water stream in ABS production

Recovery of terephthalic acid in PTA plants

PTA crystals are large and fast filtering solids and concentration in the mother liquor after crystallization is relatively high. Recovery is carried out with centrifuges or rotary pressure filters. However, while cooling the filtrate, additional PTA is precipitated in considerable amounts and this would be lost in the waste stream if no treatment were to follow. Additionally, the organic load in the wastewater stream would significantly contribute to the COD level downstream in the biological treatment system. The FUNDABAC filter helps to reduce organic waste and increases yields by up to 2% in PTA plants.

Dry PVC cake discharge

Dry PVC cake discharge

Process water recovery

CaSO4 removal in Chlorine Alkali processes

Absorption column wash water filtration

Absorption columns for gas treatment are widely applied to effectively remove contaminants. Solids are removed and accumulate in the wash water. For many years the FUNDABAC filter has played an important role in removing solid contaminants from absorption liquids in coal fired power plants, waste incineration plants and refineries (H2S removal).

Treatment of the flushing water of electrostatic filters

Electrostatic filters applied in flue gas treatment processes need to be flushed regularly for regeneration. Without an appropriate solid/liquid treatment system, the used flush water would have to be rejected, producing significant amounts of waste. The FUNDABAC filter is ideally suited for this application and allows for a closed loop design in unmanned operations, virtually eliminating liquid waste.

Waste water recycling in PVC production

Wastewater in PVC plants cannot be recycled unless COD is reduced and solids are completely removed. The FUNDABAC filter represents a creative solution for this specific stream.

DrM, Dr. Mueller AG, established in Switzerland in 1982, is a global leader in the supply of solid-liquid separation systems. Over 3,500 filtration systems have been installed worldwide to date, successfully operating in hundreds of industrial applications. The material presented above represents a very small cross-section of applications in which DrM candle filters have been successfully employed.

DrM’s core products are its FUNDABAC and CONTIBAC candle filters, sophisticated systems capable of removing suspended solids, measuring 1 micron or less, from liquid streams. As shown in the photos, vertical filtration elements (candles) are installed inside a pressure vessel. A textile filter cloth is fixed over the length of each candle using a simple, circular fixation clamp. DrM’s clamp design more successfully prevents liquid leakage compared to competitive clamp designs.

DrM filters operate in a fully automatic fashion and do not require operator intervention. Due to the absence of moving parts, maintenance is simple and limited to the periodic replacement of inexpensive filter cloths, in many cases an annual maintenance task. DrM offers its clients in excess of fifty different types of filter cloths, each one capable of finely adapting to the very specific requirements of a given application. The proprietary design of DrM candles provides FUNDABAC filters the unique capability of discharging filtered solids as a 50-80% dry cake, thus minimizing the amount of waste to be disposed.

For further information contact:
DrM (Dr. Mueller AG)