Water & Wastewater Asia Nov/Dec 2018

Water & Wastewater Asia • November / December 2018 IN PERSON | 17 WHY HONG KONG CHOSE DE NORA’S CECHLO-OSCG TECHNOLOGY The decision for a territory-wide conversion by the Water Supplies Department (WSD) under the Hong Kong government was made to address safety concerns associated with liquid chlorine containers being transported and stored around highly populated waterworks. The selected De Nora CECHLO system is an ion exchange membrane electrolytic technology which is used to produce chlorine gas and a 12.5 per cent high-concentration hypo on site. Each of the potable water treatment plant will have a combined generation capacity of 16.9 tonnes of chlorine per day. All systems are expected to be operational by 2020. CHO Ping-ho, chief electrical and mechanical engineer/maintenance of theWSD, tells WWA the reasons behind their choice of water disinfection system. Q: Whydid theWater SuppliesDepartment of Hong Kong choose De Nora? PH: An in-house review by WSD on the feasibility of local generation of chlorine for the use in water treatment works in Hong Kong has been conducted recently. It was revealed that small-scale chlorine generation plant is more readily available in the commercial market, which makes local generation of chlorine technically viable. Since the use of chlorine for water disinfection is technically proven and cost- effective, other disinfection solutions have not been considered in the review. De Nora was proposed by the contractors for compliance withWSD’s technical specifications and safety requirements given in the contract. Q: What is the amount of chlorine needed in each water treatment plant in Hong Kong daily and where does Hong Kong purchase chlorine from? PH: An average of 6 tonnes of chorine was used per day by the water treatment works in Hong Kong. Since there is nochlorinemanufacturer inHong Kong, we usually import liquefied chlorine from the Mainland, in cylinders and drums. Q: Whydid theWater SuppliesDepartment decide to switch to chlorine generation? PH: The biggest concern has always been safety. Benefits of an OSCG plant will be a reduction or elimination of liquid chlorine that needs to be stored and transported. Our quantitative risk assessment showed that there is some risk in the transportation and storage of liquefied chlorine, mostly safety concerns on chlorine gas leakage as there are indeed some possibilities, so we decided to have local generation of chlorine gas to do away with the safety issues. We are always looking for a more reliable source. The problem with our suppliers from the Mainland is that sometimes we have fluctuation in supply. Chlorine generation technologies have improved generation by generation, and technologies nowadays can scale down to a suitable size to be installed in our water treatment plant. Before switching to chlorine generation, in order to cope with fluctuation in supply due to delay in delivery or other unforeseen events, a stock level of chlorine sufficient for 90 days’ consumption had to be maintained. With this new system, we can generate and produce chlorine any time we want. WWA We believe that demand from our customers for environmentally friendly products will continue to grow in this region as we help companies attain their environmental objectives, through reducing water consumption and easing the shortage of clean usable water through water re-use. De Nora has a range of solutions with varying levels of cost and sophistication for this reason – to provide attainable options for different markets to take the steps necessary to adopt solutions. Q: What are the benefits of using alternative disinfection technologies?Onwhat basis should clients consider adopting them? MO: Over the years, disinfection using gas chlorination, being the less capital expensive, has been the most common water treatment option in developing countries, but with potential health hazards. As legislation gets increasingly stringent aroundmaintaining low levels of residual chlorine, more countries are open to adopt on-site generation of chlorine and hypochlorite (in short electrochlorination) as part of their municipal water supply process. Q: What is the future like for alternative disinfection technologies? MO: A key trend we foresee will be that as we face increasing pressures on our limited water resources, there will be an increasing focus on alternative water sources, like water reuse. Potable and non-potable water reuse will eventually be essential to meet global demand, especially when approaches like water use efficiency and consumption reductions are maximised. However, in order for reclaimed wastewater to be considered safe, the application requires the removal of Contaminants of Emerging Concern, or CECs, also referred to as micro-pollutants. This represents opportunities for solutions including the Biologically Active Filter (BAF), a well-known technology which can be combined with ozone to remove micro-pollutants from wastewater and related issues for water reuse applications. WWA