A strong understanding of the effluent treatment process is central for effective industrial wastewater management. In any industry that uses massive quantities of water as part of their processes, there is a need to process the resulting effluent to remove contaminants before discharge and disposal. Effective effluent treatment is needed to comply with environmental regulation but can also be used to recover clean water and valuable materials for reuse.
The challenges of industrial effluent treatment
Many industries are massive water consumers and the effluent streams from water intensive industrial processes are often complex and challenging to treat. Because the exact composition of the industrial effluent can vary greatly from industry to industry or even between different processes in the same industry, industrial effluent treatment must often be customized to the specific site and process. In addition, many of the compounds found in industrial effluent are harsh and difficult to treat, requiring frequent cleaning and maintenance of the treatment equipment.
Industrial effluent composition
Industrial effluent often contains a complex mixture of contaminants that require special treatment, including suspended solids (e.g. sand, silt and microorganisms), dissolved substances, heavy metals and biological or chemical compounds, resulting in wastewater with high biological oxygen demand (BOD) or chemical oxygen demand (COD). Many of these compounds are hazardous and insufficiently treated industrial effluent is a major source of pollution which has prompted authorities in many regions to impose strict quality requirements for any industrial wastewater that is discharged into municipal water streams.
The complex nature of industrial effluent composition is one of the most significant reasons why industrial effluent treatment is often such a challenging task.
The stages of industrial effluent treatment
Typically, an industrial wastewater treatment process consists of several steps of effluent treatment. This is commonly referred to as primary, secondary and tertiary treatment, and additional treatment technology may be involved both before and after these stages. Each treatment step serves a specific purpose in the effluent treatment process:
Before entering the treatment process, the effluent is typically filtered and screened to remove larger residue and solids, such as plant material, dirt and other impurities. Pre-treatment can also include flow equalization or segregation where needed.
During primary treatment, the effluent is allowed to settle so suspended particles can sink to the bottom as sediment. In some cases, chemicals are added to coagulate the impurities.
In the second stage of the effluent treatment process, bacteria are used to accelerate the decomposition of bio-degradable organisms in the effluent. This process can take place both with or without the presence of oxygen (aerobic and anaerobic effluent treatment, respectively).
Tertiary treatment includes filtration and removal of microscopic compounds. This includes techniques like sand or disk filtration, active carbon adsorption and disinfection using chemicals or ultraviolet (UV) light.
Once the effluent has been through primary, secondary and tertiary treatment, there are many options for advanced treatment. This includes thermal or membrane-based evaporation, reverse osmosis treatment, Minimal or Zero Liquid Discharge (MLD/ZLD) and recovery of water and valuable resources, such as salts.
Advanced treatment also covers technologies for brine concentration, such as membrane and thermal technologies as well as membrane distillation which is a hybrid between membrane and thermal. Membrane technologies include electrodialysis, RO and FO. Examples of thermal technology are multi-effect distillation, multi-stage flash and vapor compression technologies covering MVR and TVR.
In many ways, ZLD is the holy grail of industrial effluent treatment. In this process, no wastewater leaves the facility and only solid waste is produced. However, while ZLD can greatly improve your effluent treatment process, ZLD systems are expensive to implement and operate. The main concern is the costly energy consumption of the thermal evaporators and crystallizers needed to remove the remaining water once the effluent has been through primary, secondary and tertiary treatment.
Before reaching the ZLD stage, the effluent must have undergone both physical, chemical and biological treatment as well as membrane filtration. Under vacuum, water is evaporated, and the concentrated brine from the membrane filtration gets further concentrated before it is sent to a crystallizer or solar evaporation ponds for final processing.
Several types of evaporators can be used either individually or in combination to reduce the remaining liquid from the brine from the membrane filtration. For example, a high-capacity multi-effect evaporator (MEE) could be coupled with an agitated thin-film dryer (ATFD). This combination is highly effective but is also energy intensive. For handling more complicated effluent streams, a dedicated low-capacity mechanical vapor recompression (MVR) evaporator may be a good option.
By implementing FO in the effluent treatment process, it is possible to achieve a much higher concentration of the effluent before it reaches the evaporator stage. At this point, complex multi-evaporator setups can often be replaced with FO in combination with a single and smaller MEE which requires considerably less energy in terms of both to operate.
USING FORWARD OSMOSIS FOR EFFLUENT TREATMENT
Billions of years of evolution have made aquaporins extremely efficient and selective. By incorporating a forward osmosis (FO) system that uses Aquaporin Inside® membranes into your effluent treatment system, you can achieve minimum or zero liquid discharge while also reducing costs.
Minimize effluent volume
FO allows you to extract more clean water from your effluent stream than any other method currently available. This reduces the volume of effluent that needs to be processed by evaporators/crystallizers in a ZLD system, allowing you to reduce your energy consumption – one of the costliest aspects of the wastewater treatment process. You can also reduce your carbon footprint by up to 40 percent.
Improve quality and quantity of water for reuse
Due to the use of aquaporins, Aquaporin Inside® FO membranes have exceptional rejection rates. The aquaporin proteins used in the membranes only allow pure water molecules to pass the effluent treatment. When combined with a TFC layer, this produces a membrane which only allows tiny quantities of pollutants to pass. This makes it much easier to manage problematic compounds which might otherwise prevent you from reusing water from your industrial process. An FO solution not only improves the quality of recycled water but makes more of it available for reuse too.
Simplify your effluent treatment
While pretreatments like primary, secondary and tertiary treatment are still required to remove heavy solids, biological matter and particles, FO can replace several complicated steps of your effluent treatment process. Depending on the specific feed composition and process, this can include the ultrafiltration (UF), nanofiltration (NF) and/or reverse osmosis (RO) stages. In few cases it can even replace the primary and secondary treatment. On the downstream side of the effluent treatment system, FO can reduce the load on ZLD evaporators and crystallizers, which in a greenfield project means that a setup which normally requires several different evaporator/crystallizer types can be replaced with a single evaporator.
Optimize land use
Industrial effluent treatment often requires vast amounts of land. But with land prices at a premium, having to devote more space for your wastewater treatment process can be a costly proposition. Especially in densely populated regions, industrial areas are already at capacity. It is therefore imperative for factories to simplify their treatment processes and optimize land use. The efficiency of Aquaporin Inside® technology enable more industrial wastewater to be processed, without increasing the physical footprint of your facility.
LIMITATIONS OF FORWARD OSMOSIS FOR EFFLUENT TREATMENT
Membrane fouling and scaling is one of the major challenges of wastewater treatment. Scales are formed when dissolved substances in the feed water reach their solubility limit. When exceeding the solubility limit, substances precipitate out of the solution and onto the membrane. Precipitate on the membrane surface results in reduced performance and frequent cleaning or membrane replacement leading to increased maintenance and operating costs. However, due to the low pressure of the feed solution and the non-existence of spacers, the hollowfiber configuration used in the Aquaporin Inside® FO membrane technology is less prone to scaling and fouling.
Performing effective industrial effluent treatment demands a reduced amount of scaling and fouling. This reduces the need for cleaning of the membrane and extends its lifetime too. However, it remains important to clean the membrane regularly. Flushing or osmotic backwash are some of the methods which can be used to clean the FO membrane.
DISPOSING OF INDUSTRIAL EFFLUENT
Discharge to municipal sewage system
Centralized wastewater treatment is typically considered the most desirable solution to meet the growing demand for clean water in growing urban centers. But most municipal sewage systems require rigorous treatment before any industrial effluent can be discharged. Even a small amount of untreated industrial effluent could cause considerable damage to the sewage system and create a risk of danger to public health. Thus, the contents of the industrial effluent must be safely treated on-site if it is to be discharged to a municipal sewage system.
Discharge to waterbodies
As a result of more than a hundred years of growing industrialization, untreated industrial effluent is every day being discharged into water bodies breaching their intrinsic carrying capacity. This creates human health and environmental crises, especially in rapidly urbanizing areas. It is therefore necessary to find out the composition of the industrial waste to ensure that the industrial effluent can be absorbed by the receiving water without damaging the aquatic environment or breaching national and international standards.
Zero or minimal discharge
Zero liquid discharge (ZLD) or minimal liquid discharge (MLD) wastewater treatment can improve water recycling, reclaim valuable resources and eliminate contaminated wastewater discharge. Here, the wastewater is treated, purified and cycled back for reuse. The remaining solid waste can safely be disposed, often after reclaiming valuable resources like Glauber’s salt. Despite all these benefits, ZLD systems are expensive to implement, are energy intensive, have high operating costs and can be challenging to maintain. In India and other developing countries, many ZLD systems run on coal, gas or other non-sustainable energy resources, increasing the already high carbon footprint. It is important to consult an experienced partner or specialist, who can assist you in designing a customized solution which fits your specific production setup, challenges, and goals.
Vacuum trucks are often used by industrial plants to handle large-scale effluent transportation when no other form of discharge is possible. Limiting trucking is often desirable as it is time consuming and expensive. Increased evaporation and filtration can reduce the need for wastewater trucking while at the same time reducing costs and carbon emissions related to truck transportation.
COST OPTIMIZATION OF INDUSTRIAL EFFLUENT TREATMENT
Reduce energy costs for evaporators
One of the major expenses of running an effective treatment system is the cost of the energy needed to power the evaporators which remove the remaining liquid from the effluent. By integrating a forward osmosis (FO) process that uses Aquaporin Inside® technology in your effluent treatment system, you can minimize waste saving costs related to disposal or evaporation.
Increase capacity of existing facilities
With land prices at a premium, having to devote more space for your wastewater treatment process can be a costly proposition. Aquaporin Inside® enable you to process more industrial wastewater, without increasing your physical footprint.
Separate streams and treat difficult streams at the source
Industry effluent can be treated with or without the segregation of effluent streams. However, with segregation, both salt and water can easily be recovered from the effluent streams. When treating the industrial effluent at the source with advanced water treatment techniques, the level of toxic pollutants is also reduced.
Reclaim valuable components
Advanced FO systems provide the possibility of capturing precious materials in your wastewater - such as nutrients, metals or Glauber's salt (sodium sulfate decahydrate) - for recycling or reuse.
Want to know more about industrial effluent treatment?
You can either visit our industrial-water hub or you can download our guide 'How to solve India's wastewater challenges with forward osmosis'.