Total solution for RO system with our RO chemical line up

Water is essential for all living beings, but water shortages around the world have been increasing in frequency and severity due to population increases and economic growth, especially in developing countries. To mitigate water shortages, reverse osmosis (RO) membrane technologies can produce fresh water from seawater, wastewater or underground water. The principle and operation of RO technologies are intrinsically simple in comparison with other separation processes, such as distillation, ion exchange and extraction. Nevertheless, water production plants still face various problems. Fouling on the RO membrane causes a decrease in the efficiency of the membrane and it becomes difficult to retain the required permeate water amount and quality. This fouling is induced by natural phenomena and human errors during operation. In particular, bio-fouling still presents a serious problem for RO operation without proper chemical treatment. However, Kurita Water Industries Ltd. has developed the innovative KURIVERTER™ Treatment Program for RO membrane facilities. This treatment has contributed to stable operation and cost minimization for many commercial plants (Matsumoto et al. 2009; Matsumoto et al. 2011; Matsumoto et al. 2013; Matoba et al. 2015; Nakamura et al. 2015). Moreover, some products can be used as novel and pragmatic approaches to emergencies. Several case studies are introduced in this paper, particularly with regard to KURIVERTER™ IK-110 with S.sensing™ B and the RC series.

The KURIVERTER™ Treatment Program covers a wide range of RO systems, as shown in Figure 1. The goal of the KURIVERTER™ Treatment Program is to optimize RO operation, minimize operating costs, and achieve the stable operation desired by all operators. It can be effectively applied from upstream down to the RO system itself as an on-line treatment program. Some products are very useful for regular off-line treatments such as cleaning. In addition, rejuvenation treatment products can eliminate RO membrane replacement in emergencies, such as membrane deterioration by chlorine leakage upstream, or frequent cleaning in place (CIP).

Kurita considers that the most important factor for stable operation is bio-fouling prevention. To prevent bio-fouling, KURIVERTER™ IK-110 with S.sensing™ B is the key technology. Actually, bio-fouling problems are still difficult to completely solve, to the distress of many operators. Numerous researchers have tried to unravel the mechanism involved in bio-fouling of a membrane surface. The consensus is that microorganisms are present in almost all water processes, and these microorganisms tend to adhere to every surface and grow by consuming nutrients accumulated in the water phase. The adhered microorganisms excrete extracellular polymeric substances (EPS), and then these EPS become bio-films (Matin et al. 2011; Mitra et al. 2009; Yang et al. 2010). Some operators assume that microorganisms flowing into RO systems should be sterilized. However, the use of potent biocides in actual plants with a bio-fouling problem poses risks to the personal safety of the operators.

KURIVERTER™ IK-110 (hereafter, IK-110) has been developed and certified by the NSF, and satisfies the guidelines for the chemical evaluation of waterworks by the Japanese Ministry of Health, Labour and Welfare. These certifications allow IK-110 to be applied to RO plants that produce drinking water without a shutdown. Also, IK-110 is not focused on ‘sterilization’ but concentrates on ‘peeling off’ and ‘prevention of bio-fouling’ on membrane surfaces (Iuchi et al. 2014). In addition, S.sensing™ B can effectively control the IK-110 dosage, depending on the degree of fouling.

The S.sensing™ application illustrated in Figure 2 is one of the tools we provide for operators. This system was developed in order to offer effective chemical treatment with visualization of the condition of a client's facilities. S.sensing™ has three features, which as listed below (also see Figure 3).

• 1.

  Easy And simple to use

  • Using the latest design trends with excellent clarity, important information can be shown on an easy-to-understand display on the portal screen. With the gadget function, users can customize and arrange the screen according to their preferences.

• 2.

  Efficient

  • Displays an overview of the status of multiple devices and equipment in the portal screen.

  • Important data can be accessed immediately, and downloading reports is easy.

• 3.

  Anywhere

  • Web Access is possible even when using mobile devices such as smartphones and tablets.

Also, S.sensing™ equipment is diversified in order to control various chemical dosages for optimization at each client's facilities. S.sensing™ B is used for RO systems.

The most characteristic slime control agent is IK-110 in the KURIVERTER™ line-up. The features and background of its development are introduced in Ref. (Iuchi et al. 2014). The first case study shows the application of IK-110 with S.sensing™ B.

This case study concerns a commercial plant in Japan that provides electricity and feed water for a high-pressure boiler, and produces drinking water in the factory by seawater reverse osmosis (SWRO). Also, operating conditions for each train are shown in Table 1. The client had tried CIP, shock treatment with sulphuric acid, and sodium bi-sulfate (SBS) to reduce the differential pressure in SWRO that was caused by bio-fouling. However, no countermeasure effectively improved the differential pressure. As a result, the client gave up trying to improve it and decided to replace the RO membranes. This plant has four SWRO trains and bio-fouling occurred in all four trains.

A comparison of flow diagrams for conventional treatment (Figure 4) and KURIVERTER™ treatment (Figure 5) is shown below. In conventional treatment, it is very common to inject sodium hypochlorite in the initial water treatment facility. However, sodium hypochlorite must be deoxidized by a reducing agent to prevent membrane deterioration. In this case study, IK-110 was substituted for sodium hypochlorite. As a result, the plant operators did not need to add the reducing agent. Also, S.sensing™ B effectively controlled the dosage of IK-110 to prevent bio-fouling.

The chemical treatment was effective for all four trains and some of the operating results are shown in Figures 6 and 7. The differential pressure decreased in all trains, and the permeate conductivity and the normalized flux also improved with our treatment. The operating cost and cost comparison were calculated based on actual data. The KURIVERTER™ application led to a 14% production increase and 28% unit cost reduction (Figure 8).

Another unique chemical product, KURIVERTER™ RC series (hereafter, RC series) is introduced here. This product is used for emergencies and is not a regular treatment, such as conventional off-line cleaning chemicals. The RC series eliminates membrane replacement because of its effectiveness in repairing deteriorated membranes by oxidation, hydrolysis at high pH and catalysis reactions by SBS and heavy metals (Nakamura et al. 2015).

A polyamide membrane contains amide bonds, but these bonds can be broken by oxidizing deterioration (Koo et al. 1986). Three chemicals constitute the RC series: RC-200, RC-300 and RC-400. RC-200 and RC-300 plug the holes caused by deterioration of the membrane surface and RC-400 enhances the stability of the coating. Figure 9 shows the mechanism of hole plugging on the membrane surface.

A commercial plant located in Japan had a wastewater reclamation system, and their RO membranes were replaced whenever the salt rejection rate became less than 92%. The cause of the deterioration was supposedly catalysis reactions involving SBS and heavy metals, Cu and Co, because these substances were present in the RO feed water. Table 2 shows the operating conditions.

An outline and the RC treatment conditions for this application are shown in Figure 10 and Table 3, respectively. CIP using an alkaline solution followed by an acidic solution was conducted before applying the RC treatment. After the CIP, the RC-200 and RC-300 solutions were added into the cleaning tank and circulated through the RO system for three hours. After circulation, the RC-400 solution was added into the cleaning tank without draining out the RC-200 and RC-300 solutions, and then recirculated through the RO system for another hour. This treatment is similar to the CIP procedure.

After applying the RC treatment, the salt rejection rate for the entire RO system was improved from 90.8% to 96.2%, as shown in Figure 11. Thus, the RC treatment helped to recover the membrane performance. Operators will be interested in the durability of the effectiveness of this treatment. Stable salt rejection was maintained for 3 months at around 97%. Some results for the salt rejection rate are shown in Figure 12. RC products on the membrane surface can normally be removed by alkaline cleaning. Therefore, it is necessary for the client to apply the RC treatment after the CIP. An operating cost comparison is shown in Figure 13. This is based on actual plant information and shows a 60% cost reduction following the RC treatment. The client assumed they had to replace their membrane due to deterioration, but they could avoid replacement, because applying the RC treatment could recover the performance. This meant that the RC treatment was capable of increasing the membrane life by a factor of three.

The KURIVERTER™ Treatment Program applied with S.sensing™ B can be the key to optimizing RO operation, minimizing operating costs, permanently stable operation, and freedom from problems currently experienced. This program covers a wide range of RO systems, and includes an on-line treatment, off-line treatment, and emergency treatment. According to Kurita, a key technology is IK-110 with S.sensing™ B for bio-fouling prevention, which is the most difficult and distressing problem for operators. Moreover, membrane replacement had previously been inevitable when the membrane had deteriorated. The RC series can eliminate the need for replacement. It is thought that the environmental impact can be reduced because disposal of membranes is not necessary. Kurita believes our treatment program will help satisfy water demand throughout the world.