Without some means of upstream scale inhibition, RO membranes and their flow passages will foul due to scale, the precipitation of sparingly soluble salts. Common examples of scale are calcium carbonate (CaCO3), calcium sulfate (CASO4), barium sulfate (BaSO4), and strontium sulfate (SrSO4). Less common but equally problematic are silica (SiO2) and calcium fluoride (CaF) scales.
Avista Technologies formulates a range of liquid antiscalant/dispersants for membrane separation systems. These formulations are designed to inhibit scale while also dispersing colloidal particles. The inhibition and dispersant properties help extend RO system run times, reduce cleaning frequencies and increase the overall productive life of the RO elements. The application of Vitec® may also eliminate the need for acid addition while maintaining desired recovery rates.
Water analysis data is unique to each treatment site so we have developed the Avista Advisor software program. Cations and anions of a water source as well as general system data are entered into the program which then recommends an appropriate Vitec® product and dosage specific to that facility.
Biological fouling of reverse osmosis membranes is one of the most challenging issues faced by operators of membrane separation systems. This is primarily due to the fact that effective biocides must be non-oxidizing in order to avoid permanent destruction of the RO membrane layer.
Avista Technologies provides two types of biocides for use in reverse osmosis systems, RoCide® DB-20 and RoCide® IS2. Both formulations are non-oxidizing and EPA registered. They are safe for use with both polyamide and cellulose acetate membranes. However, they are not for use in systems producing potable water. Both have outstanding environmental properties, degrading rapidly and naturally. This property has made them the chemical of choice, especially for systems operating under strict environmental and discharge regulations.
Shock Treatment and RO Cleaning Applications:
RoCide® DB-20 is a 20% liquid solution of the active ingredient DBNPA. This formulation is used as an intermittent feed for "shock treatment" control or it can be added to a low pH cleaning solution to kill bacterial fungi and algae in membrane systems.
Continuous Injection Biocide:
RoCide® IS-2 is based on a 1.5% isothiazoline mixture. It's a broad-spectrum formulation for use against microbiological contaminants commonly found in RO applications including bacteria, fungi, and algae. RoCide® IS-2 is designed for continuous injection into the RO feedstream to provide constant biological control.
All membrane separations systems require regular cleaning in order to maintain consistent production and optimal membrane life. The symptoms of RO fouling include a decrease in normalized permeate flow, an increase in salt passage, and an increase in differential pressure. Severe element fouling can lead to irreversible membrane damage and can render cleanings difficult or impossible.
Avista Technologies formulates a wide variety of liquid and powder cleaners to address all of the foulants common to RO systems. In addition, our laboratory personnel use an array of equipment and methods to identify the distinct constituents of unique foulants from samples submitted to us for analysis. With these results, we can recommend a specific cleaning regimine or formulate custom cleaners specific to a particular application or geographical region.
Coagulants & Flocculants
Colloid and silt fouling are the major causes of loss in performance of membrane separation systems. For this reason, many system designs include upstream multimedia filtration which involves a variety of mechanisms to achieve particle removal. When added to the feedwater, RoQuest® coagulants neutralize the negative electrostatic charges on both particles and filter media surfaces. Elimination of these charges makes collisions and attachments between particles and media grain surfaces possible.
Avista Technologies formulates a variety of liquid coagulant/flocculant chemicals under the RoQuest® name. RoQuest® 3000 is an organic polymer while the RoQuest® 4000, 5000, and 6000 are a blend of organic coagulants and ferric sulfate.
RoQuest® formulations change the behavior of particles and colloids which normally exhibit negative charges in naturally occurring feed waters. Because like charges repel each other and unlike charges attract each other, the addition of the positively charged RoQuest® polymer allows the negatively charged particles to clump together. This creates larger particles which are more readily retained in the multimedia filter (MMF), resulting in improved MMF filtration.
In addition to the main product line, Avista offer a small selection of ancillary products which may be required for efficient operation of a membrane system. These include chlorine scavenger, a salt rejection improvement aid and a range of line corrosion inhibitors. For hybrid systems, a thermal antiscalant is also offered. The products are outlined below.
In many cases, chlorine is present in the membrane plant feedwater by either direct or indirect injection. Municipal feedwaters typically contain some level of chlorine residual and water treatment plants inject chlorine in order to reduce biological activity in the pretreatment process. Because polymaide membranes have very little tolerance to chlorine and other oxidising agents, the chlorine must be de-activated to prevent permanent membrane damage. Anti-Chlor 30 is a 30% solution of sodium bisulphite and functions as a chlorine scavenger. The product addition rate may be calculated using Avista Advisor 3.
Membrane Sizing Agents:
Polyamide membranes may lose some of their rejection charerecteristics as a result of oxidation or simply due to age. Phoenix liquid and powder resizing agents are available to coat the surface of partially oxidized/damaged polyamide membranes and improve salt rejection. Elements should always be cleaned prior to sizing.
Reverse osmosis permeate is often corrosive to downstream piping due to a low level of hardness and alkalinity. In the case of permeate from a seawater plant; the level of chloride will be disproportionately high. Corrosion may be prevented by applying a suitable inhibitor. The ViCoat product range includes formulations based on inorganic pyrophosphate, silicates and silicate/polyphosphate blends.
Vitherm 700 is a blended antiscalant developed for use in thermal distillation systems. Low application rates of Vitherm 700 are effective in preventing scale and metal oxide precipitates over the full range of operating temperatures.