Green initiatives to solve RP water problems: Membrane science and technology for wastewater recycling and reuse

(Second of two parts)

How are we going solve water scarcity when all our water resources are contaminated and continuously being depleted? What is the best alternative to get fresh water? Is it by “drilling wells for water like oil” which involves substantial financial outlay, and possible draining and destruction of the Earth’s crust? I do not see any other options but to recycle and reuse our wastewater. Are we “psychologically” prepared to use even our own sewage as source of drinking water? In my opinion, we should be and it is now a MUST. Recycling sewage water is now common in areas with water shortages in the US, Australia and other countries in Europe.

For instance, NASA developed a water-recycling device for the International Space Station (ISS) that will process the astronauts’ urine for communal consumption. Basically, this device is similar to a sewage treatment plant that can purify urine in several steps so that it can be reused for drinking, food preparation and bathing. The device can recover about 93 percent of the initial wastewater fed into it and could reduce the amount of water generated by a visiting spacecraft by 6,803 kg per year. “The water from the system will be cleaner than US tap water. Rationing and recycling will be an essential part of daily life on the ISS.” (Astronauts Tackle Glitches with Space Water Recycler http://www.livescience.com/space/ 081121-sts126-waterrecycler33-glitch.html).

Therefore, like the astronauts, to meet the domestic and industrial water needs of our country, there is an urgent need for us to look into tapping water from non-traditional sources like our wastewater and even floodwater. Very soon, due to the ever-tightening water regulations, municipalities and industries will have to look into innovative technologies to ensure the highest quality drinking water for the community and also wastewater that is safe for disposal.

Membrane-based technologies such as ultrafiltration (UF) and microfiltration (MF) for water purification, and membrane bioreactor (MBR) technology for wastewater treatment have been accepted worldwide by various industries. UF and MF are cross-flow filtration processes that use high cross-flow rates to enhance permeate passage and reduce accumulation of solute on the membrane surface (also known as fouling). The permeate is the liquid that passes through the membrane. With membrane technology, the supply of safe, clean and affordable water for communities and businesses, such as agriculture and industry, will be sufficient.

Ultrafiltration (UF) is a low-pressure (5-150 psig) membrane separation process for separating larger size solutes or macromolecules such as protein from the aqueous solutions by means of a semi-permeable membrane. The UF membrane, with pore size ranging from 0.005 to 0.1 micrometer, can produce potable water free of large viruses, bacteria, parasites, Cryptosporidium, Giardia, suspended solids and turbidity. These UF systems consistently produce high-quality water that exceeds government drinking water regulations, regardless of the drinking water source. The UF process makes chlorine a more effective post-treatment disinfectant and, therefore, reduces chemical consumption. In 1992, in Littleton, Massachusetts, the high levels of iron and manganese in their highest volume well made their water virtually unusable. Littleton selected an ultrafiltration system, after extensive pilot studies, to remove iron to a non-detectable level and manganese to below 0.02 ppm. A 99.9-percent recovery with no waste discharge was achieved — which was critical, as Littleton had no sewer or waste treatment facilities. Microfiltration (MF) is a low-pressure (10-100 psig) process that retains large suspended solids, such as particulate matter, and passes some suspended solids and all dissolved material. The retained solids do not accumulate on the membrane surface. The pore size of an MF membrane ranges from 0.1 to 3 micrometer, therefore, MF does not allow passage of bacteria.

With my interest to determine the best membrane technology to solve the Philippines’ water problems, I consulted Dr. Andrew Benedek, a Canadian researcher and successful technopreneur. He is the first winner of the Lee Kuan Yew Water Prize in Singapore (March 19, 2008), which is an international award recognizing an individual or organization for outstanding contributions in the world of water management. “Dr. Andrew Benedek is held in high esteem by the global water industry community for his pioneering work in low-pressure membranes. Low-pressure membranes use less energy, have lower operating costs and greater ease of operation compared with conventional water purification technologies. The widespread adoption of low-pressure membranes has made the technology even more affordable.” (An Interview with Lee Kuan Yew Water Prize Winner Dr. Andrew Benedek, http://ww.pennnet.com/Articles/Article_Display.cfm? ARTICLE_ID=328720 &p=41).

According to Dr. Benedek, in his message dated Feb. 7, 2008, the most cost-effective application of membranes today is water reuse or distributed systems. Treatment of sewage wastewater using membrane bioreactor (MBR) technology can essentially produce drinking water in one simple and reliable step. In treatment of water where the distribution is not yet in place, small point-of-entry systems with membranes can be used to avoid the building of an expensive distribution network. With a membrane bioreactor, recycling sewage wastewater and supplementing it with rainwater can produce safe drinking water that does not require water and sewage distribution lines. For treatment of rainwater or other sources of water, a simple membrane system can be used to provide clean and safe water that requires very little maintenance, and costs much less than a central system.

Therefore, to meet the need for water and sanitation in a developing country like the Philippines, reuse and decentralization will be essential. Membrane bioreactors will be an essential part of advancing such water sustainability, because they encourage water reuse and open up opportunities for decentralized treatment. Currently, there is a mobile wastewater treatment membrane system for a wide range of municipal, industrial and domestic clients. These systems can be used as an alternative source of water supply in emergency conditions, for instance, during drought or after massive flooding like the one brought by tropical storm “Ondoy.”

Membrane bioreactor (MBR) is an advanced technology which is a combination of a biological treatment process and biosolids separation by membrane filtration. The system can process water that meets stringent effluent discharge requirements, eliminates solids, reduces wastewater discharge fees, and requires less space than conventional wastewater treatment. MBRs are considered the “best available and successful technology” for the treatment of both municipal and various industrial wastewater such as paper mills, beverage ingredient processors, slaughterhouses, food processors, chemical plants, tank truck cleaning operations, pharmaceutical, electronics, mining and petroleum processing. Typically, the discharge from a conventional plant will contain 10,000 to 100,000 microbes per milliliter. (Comparing Wastewater Treatment Technologies, http://www.kochmembrane.bncom /mbr_basics.html). Membranes act as a barrier to bacteria and suspended solids to produce a low turbidity treatment plant effluent with very low bacteria counts. 

MBR systems have been installed at thousands of municipal wastewater treatment plants (WWTP) of all sizes in many countries, and have serviced a wide variety of challenging industrial wastewater applications. A MBR plant constructed in a warm climate will be less costly than one with an identical capacity located in a cold climate. Therefore, since the Philippines has a warm climate, the technology is cost-competitive in our country. A MBR plant has a treatment capacity of around five to 10 million liters per day (ML/d), while the next generation has design capacities of up to 45 ML/d. Since sludge settling is not required, MBRs can operate at much higher mixed liquid suspended solids (MLSS) concentrations, typically in the range of 8,000 to 15,000 mg/L, enhancing the system’s ability to remove nitrogen and enabling it to operate in a relatively small bioreactor volume. In the City of Redlands, Los Angeles, California, MBR technology is the only way to establish an efficient and effective water-recycling program that will conserve their potable water supplies. Recycled wastewater produced by their 6.6 million gallons per day MBR facility can supply more than enough water for the cooling towers at a new power station, and irrigation water for some local agricultural and recreational sites.

We all drink water, therefore, each one of us has a moral responsibility to conserve and keep our water resources clean and safe. Hence, let us recycle the wastewater that we produce and reuse it to solve water scarcity and prevent further contamination of our water resources. A sustainable resource for irrigation, agriculture, and industrial processes is to use reclaimed or repurified water. Water reuse also reduces wastewater discharge to lakes, rivers and oceans, making it an environmentally friendly option. Collection of rainwater to supplement the recycled water is also necessary. These are the green initiatives that will help reduce water usage and solve our water problems.

* * *

Dr. Michelle C. Almendrala is a faculty member of the School of Chemical Engineering and Chemistry of the Mapua Institute of Technology. She is a Fulbright Senior Scholar currently doing advanced research in “Recycling of Biobutanol Fermentation Broth by Membrane Ultrafiltration” at the Department of Chemical and Biomolecular Engineering of the Ohio State University, Columbus, Ohio, USA. Her research work includes fermentation of biobutanol from glucose and corn stover, clarification of fermentation broth using membrane ultrafiltration, and recovery of biobutanol from the broth by gas stripping and pervaporation. Her interests are membrane separation applications in wastewater treatment and recycling, rice bran oil extraction, and fruit juice clarification using hollow fiber membranes. E-mail her at [email protected].