From oil and grease to phenols, metals, suspended solids and other organic compounds, there is a wide range of substances present in industrial wastewater across the Middle East.
Many companies employ state-of-the-art treatment processes to ensure that their wastewater presents no danger to the public or the ecological balance of receiving waters. However, some firms simply discharge their waste into the nearest municipal sewer. Times are changing for these companies, though.
Traces of metals, such as zinc, are increasingly being found in domestic wastewater and can affect the environment
Municipal water is increasingly being recycled and facilities are not designed to remove all the substances that come from industrial activity. Utility providers tell MEED that traces of metals, such as zinc, are increasingly being found in wastewater and can have a significant impact on aquatic life and the environment.
Enforcing wastewater treatment
Water authorities are clamping down on industries and are demanding that water be treated before it is discharged. Enforcement, which has historically been lacking in this area, is being strengthened as the role of environmental regulators in the region grows.
In the UAE, Abu Dhabi introduced its Trade Effluent Control Regulations in June 2010. These require all industries discharging into the Abu Dhabi sewerage system to hold a consent licence. The terms of the consent make it clear that hazardous, radioactive and medical waste cannot be put into the system, and place limits on other materials. Non-hydrocarbon oils, for example, must not be present in quantities greater than 100 milligrams a litre (mg/l), and total suspended solids must not exceed 500mg/l.
The build-up of selenium in wastewater is a growing concern due to its detrimental impact on the environment
For some industries this is not a problem, as they have been treating their wastewater for years. For others, it signals a new development. Wastewater experts tell MEED the first step to compliance is identifying exactly what is in the effluent. “You have to start with a regimented characterisation programme to figure out what else is in the water, as it is not just the contaminant that you are treating,” says Jamal Shamas, head of the global sector of US consultant CH2M Hill’s water for oil and gas business. “Other contents could affect the treatment process and make it work less efficiently or not work at all.”
For large industries, Shamas recommends testing the concept design. “You need to have a proof of concept. Would that treatment process work or is there anything in the water that would stop it working properly? If you want to do it right, you can take it to a pilot test scale.”
Other experts agree that understanding the composition of the discharge is the first step in the process chain. “We have to understand the specifications and pollutants in the water,” says Ilham Kadri, commercial manager for Europe, the Middle East and Africa at Dow Water & Process Solutions, a division of the US’ Dow Chemical Company. Once this identification is made, the treatment regime usually consists of a chain of activities designed to target certain substances and achieve prescribed quality criteria.
“You can start with clarifiers to remove oil and grease and follow that up with ultra-filtration or nano-filtration where we remove organic materials,” says Kadri. “Then you go to reverse osmosis technologies and this can also be combined with our ion-exchange resin if you would like ultra-pure water.”
The substances to be removed will vary from company to company. “Each industry has different pollutants,” says Bassem Halabi, group business development director at UAE-based water management company Metito. “For the petrochemicals industry, for example, phenols can be quite common.”
Phenols are chemical compounds that come from the catalytic cracking process. They are toxic to aquatic life, harmful to human health and deplete oxygen levels in receiving waters, causing changes to ecosystems. Removal is usually achieved with biological (secondary) treatment. “Most phenolic compounds are highly biodegradable if the biological system is designed properly,” says Shamas. “If low levels cannot be attained using biological treatment, polishing with carbon filters may be necessary. Advanced oxidation techniques can also be used to reduce levels of high-strength phenolic streams.”
Phenols can also be found in wastewater from the steel industry, where cyanide and ammonia are also present. Highly toxic cyanide is removed with advanced oxidation techniques that break it down into non-toxic components.
Ammonia can be removed from wastewater with a biological treatment involving ammonia-eating bacteria, which convert ammonia to nitrates. This process is called nitrification and can be particularly useful to the oil and gas sector, where wastewater often contains nitrates.
Nitrates can in turn be converted into harmless nitrogen gas in a process called denitrification, using nitrate-loving bacteria grown under very low or zero levels of dissolved oxygen in water. Nitrification and denitrification can achieve total nitrogen removal, ensuring wastewater discharged to receiving streams has less of an impact on the environment.
Selenium increase in wastewater
The build-up of selenium in wastewater is another growing concern. It can be found in a variety of forms from metal sulphide ores to selenium salts. As a result, selenium can be found in wastewater from the oil and gas industry, the glassmaking industry and copper production.
“There is a concern about selenium that hasn’t really hit the Middle East yet,” says Shamas. “It has been on the radar since the early 1990s, but additional ecological studies and new data and testing mean that agencies have adjusted their criteria for this substance.”
Removal of selenium is complicated because it can be present in various forms, making it more difficult to target. But its detrimental impact on bird life and ecology makes its removal increasingly necessary. Successful treatment methods include advanced biological treatment, chemical addition and ion exchange.
Metals can be a side-effect of processing industries and must be removed using chemical or physical processes rather than biological treatment. “If the metals are in a particulate state you can use anything that removes particulates to reduce their levels,” says Shamas. “But metals are not always present in particulate form; most of the time they are in a soluble form.” Treatment therefore requires converting them to particles that can be removed by conventional and advanced solids-separation techniques, such as gravity separation, sand filtration or membrane processes.
Soluble metals in relatively clean water can also be removed by ion-exchange resins. Contaminated water is passed through a column packed with a resin made up of porous beads with a diameter of less than 1.3 millimetres. These beads host chemically active sites that allow specific elements on the resin to exchange their sites with contaminants in the wastewater. When the resin becomes saturated with the contaminant, it needs regeneration where the active sites are replenished and the contaminant is desorbed from the resin into a concentrated solution for disposal.
“Ion-exchange resin can selectively extract one component, and can be used in industrial wastewater requiring trace-contaminant removal, for example in the nuclear power industry,” says Kadri. “We use the resins to remove trace contaminants, such as radium, arsenic and perchlorate.” The method is also used to prepare water for reuse and to polish potable water for special applications. “For the electronic and semi-conductor industry, ultra-pure water is needed, and here you need ion exchange for polishing,” says Kadri.
Understanding the effect of these wastewater streams on the environment is another area benefiting from current research. As environmental regulators become more aware of the impact of certain substances, they are tightening water-discharge requirements. Although industries around the world have been carrying out secondary-level treatment for decades, pollution from contaminants that are harder to remove has been building up, says Shamas, and this presents new challenges. “Industries are not addressing the next level of organics and metals, so there is a lot of inbound bio-accumulation in marine life,” he says.
It is not only the prevention of pollution that is driving industrial treatment improvements. The need to recycle water is also encouraging more research into contaminant-removal processes.
In Qatar, the US-based ConocoPhillips’ Global Water Sustainability Centre (GWSC) at the Qatar Science & Technology Park is working on the development of solutions for treating and recycling by-product water from oil and gas operations. Its work focuses on the reuse of formation water, which comes to the surface with oil and gas in petroleum reservoirs.
ConocoPhillips estimates that exploration and production operations yield three to four barrels of produced water for each barrel of oil generated, and the volume of this formation water can increase over time as the oil or natural gas is depleted. However, this water is usually highly saline and may contain hydrocarbons or minerals from the reservoir. Treating this water to a useable standard is a priority for the GWSC, which opened in April 2010.
With a better understanding of the ecological implications of contaminants in industrial discharge, authorities across the region are becoming more vigilant. Regulations are becoming stricter and industries producing wastewater must now re-examine their methods and techniques to comply with the laws and to minimise contamination and environmental impact.