In the wastewater, there are total solids (TS), which are made of all measurable solids present in the effluent. There are two components of TS: insoluble, suspended solids (Total Suspended Solids, TSS) and dissolved solids (Total Dissolved Solids, TDS).
The TDS indicates the amount of all inorganic and organic substances present in the wastewater. Basically, it includes everything present in water other than pure H2O and suspended solids. Sulfates and chlorides are the primary pertinent components in tannery effluents; TDS is frequently referred to as salinity or salt informally.
The Zero Liquid Discharge (ZLD) wastewater treatment technology can eliminate the problem of high TDS effluent in the wastewater and make it reusable. It can remove all dissolved solids on-site and reclaim reusable water. The aim of the ZLD process is to concentrate dissolved solids in the wastewater until only one solid damp waste remains. Solid waste is disposed of off-site, and nearly all water is reclaimed and reused.
The ZLD treatment process can be used as an advanced wastewater treatment constituents to produce by-products that are more easily biodegradable while lowering overall toxicity, pH, COD, TDS, SS, and BOD parameters. According to the study results, the 99% TDS, 100% COD and BOD, and 98% SS and TSS were reduced (removed), make it Zero liquid discharge. The ZLD plant produced high-quality water that was suitable for recycling on-site, resulting in reduced water consumption.
A Zero Liquid Discharge treatment system leverages various advanced technological water treatment processes to reduce liquid waste at the end of your industrial process to zero. It is the right solution to meet all the wastewater guidelines and environmental compliance regarding discharge. ZLD systems are mostly based on standalone thermal/evaporative processes, membrane processes, or a combination of the two, referred to as hybrid systems. These systems provide additional value, ease of operation, and lower operating costs. The ZLD treatment system will be able to handle:
The high TDS levels in the wastewater can arise due to a large proportion of dissolved salts and minerals. These are the most common major constituents that contribute to the high total dissolved solids basis in these waters:
Generally, NaCl is present as a high constituent in the wastewater of industrial plants. From tens of thousands to over 200,000 mg/L, the concentrations might vary greatly. While high sodium chloride concentrations can make the water extremely salty, they also greatly increase the likelihood of corrosion and scaling issues in pipelines and process equipment.
After NaCl, calcium and magnesium salts are present in substantial quantities in high TDS water. As we mentioned above, they are mostly present as chlorides and sulfates. These ions cause pipe and equipment scaling and are directly responsible for water hardness. CaSO₄ and MgSO₄ present a unique challenge since they are less soluble and more likely to precipitate as scale.
In comparison to calcium and magnesium, these ions induce scaling at a much lower level. Sometimes, they create carbonate scales under certain conditions, particularly if the water is supersaturated with respect to calcium carbonate.
The TDS value can be high due to the presence of high levels of heavy metals as well including Fe, Mn, Pb, and As. These metals could come from the geologic formation itself or infrastructure corrosion. The presence of these contaminants makes treatment processes more difficult and is an environmental and health concern if the water is disposed of improperly.
Apart from the inorganic salts, the high TDS in wastewater can also arise due to different types of organic compounds. These consist of naturally occurring organic acids, volatile organic molecules, and liquid hydrocarbons. Due to their propensity to disrupt the treatment process or result in environmental issues, these kinds of compounds add complexity to the water.
The zero liquid discharge treatment technology involves multiple forms of treatment, including physical, chemical, and sometimes even biological methods. Here are the key technologies used by ZLD for the removal of TDS:
At this stage, simple things from the wastewater are removed through basic filtration, or they are precipitated out. The wastewater is also conditioned with the reduction of suspended solids and materials that would otherwise scale and foul further treatment steps. The ZLD treatment block includes a reactor or clarifier of some kind to precipitate out silica, hardness, and metals.
In this stage, the concentration occurs with membrane-based technologies like reverse osmosis (RO). RO is amongst the most used technologies for TDS removal. RO functions by pushing water over a semipermeable membrane that lets water molecules flow through but keeps out the majority of dissolved minerals, salts, and other impurities. After the process is finished, concentrated brine streams with the rejected salts and impurities and a permeate stream with significantly lower TDS are produced.
This is the last stage where a solid is generated through thermal processes or evaporation, where you evaporate all the water off, collect, and reuse it. The rest of the wastewater will go to the crystallizer, which continues to boil off all the water until all the impurities in the water crystallize and are filtered out as a solid.
Handling high TDS in wastewater has become one of the most crucial tasks in wastewater treatment, and ZLD is the most reliable technology for this purpose. At WiproWater, we have developed expertise in high-TDS water treatment for various industrial plants. We provide advanced-tech treatment solutions to meet the specific needs of wastewater treatment.
Our reputation in the design and delivery of advanced water treatment systems empowers operators to improve operational efficiency. Let us know your requirements.