RO/DI Water Systems
/ By Panorama Consulting & Engineering Inc. / System design • Utility Optimization • Waste Reduction/ 0 Comments

RO/DI Water Systems

RO/DI stands for Reverse Osmosis and Deionization. The product is a multi-stage water filter, which takes in ordinary tap water and produces highly purified water.

Tap water often contains impurities that can cause problems. These may include phosphates, nitrates, chlorine, and various heavy metals. Excessive phosphate and nitrate levels can cause an algae bloom. Copper is often present in tap water due to leaching from pipes and is highly toxic to invertebrates. An RO/DI filter removes practically all of these impurities.

There are typically four stages in a RO/DI filter:

  • Sediment filter
  • Carbon block
  • Reverse osmosis membrane
  • Deionization resin

If there are less than four stages, something was left out. If there are more, something was duplicated.

The sediment filter, typically a foam block, removes particles from the water. Its purpose is to prevent clogging of the carbon block and RO membrane. Good sediment filters will remove particles down to one micron or smaller.

The carbon, typically a block of powdered activated carbon, filters out smaller particles, adsorbs some dissolved compounds, and deactivates chlorine. The latter is the most important part: free chlorine in the water will destroy the RO membrane.

The RO membrane is a semi-permeable thin film. Water under pressure is forced through it. Molecules larger/heavier than water (which is very small/light) penetrate the membrane less easily and tend to be left behind.

The DI resin exchanges the remaining ions, removing them from the solution.

There are three types of RO membrane on the market:

  • Cellulose Triacetate (CTA)
  • Thin Film Composite (TFC)
  • Poly-Vinyl Chloride (PVC)

The difference between the three concerns how they are affected by chlorine: CTA membranes require chlorine in the water to prevent them from rotting. TFC membranes are damaged by chlorine and must be protected from it. PVC membranes are impervious to both chlorine and bacteria.

Reverse osmosis typically removes 90-98% of all the impurities of significance to the aquarist. If that is good enough for your needs, then you don’t need the DI stage. The use of RO by itself is certainly better than plain tap water and, in many cases, is perfectly adequate.

RO by itself might not be adequate if your tap water contains something that you want to reduce by more than 90-98%.

A DI stage by itself, without the other filter stages, will produce water that is pretty much free of dissolved solids. However, DI resin is fairly expensive and will last only about 1/20th as long when used without additional filtration. If you’re only going to buy either a RO or a DI, it would be best to choose the RO, unless you only need small amounts of purified water.

Duplicating stages can extend their life and improve their efficiency. For example, if you have two DI stages in series, one can be replaced when it’s exhausted without producing any impure water. If you have both a 5-micron sediment filter and a 1-micron filter, they will take longer to clog up. If there are two carbon stages, there will be less chlorine attacking the TFC membrane. Whether the extra stages are worth the extra money is largely a matter of circumstance and opinion.

RO/DI capacities are measured in gallons per day (GPD), and typically fall within the 25-100 GPD range. The main difference between these units is the size of the RO membrane. Other differences are (a) the flow restrictor that determines how much waste water is produced, (b) the water gets less contact time in the carbon and DI stages in high-GPD units than low-GPD units, and (c) units larger than 35 GPD typically have welded-together membranes.

As a result of the membrane welding and the reduced carbon contact time, RO membranes larger than 35 GPD produce water that is slightly less pure. This primarily affects the life of the DI resin.

Most aquarists won’t use more than 25 GPD averaged over time. If you have a decent size storage container, that size should be adequate. A higher GPD rating comes in handy, however, when filling a large tank for the first time or in emergencies when you need a lot of water in a hurry.

The advertised GPD values assume ideal conditions, notably optimum water pressure and temperature. The purity of your tap water also affects it. In other words, your mileage will vary.

An RO filter has two outputs: purified water and wastewater. A well-designed unit will have about 4X as much wastewater as purified water. The idea is that the impurities that don’t go through the membrane get flushed out with the wastewater.

There is nothing particularly wrong with the wastewater except for a slightly elevated dissolved solid content. It may actually be cleaner than your tap water because of the sediment and carbon filters. Feel free to water your plants with it.

Design of Water Reclamation System
/ By Panorama Consulting & Engineering Inc. / Sustainable Engineering • System design • Waste Reduction/ 0 Comments

Water reclamation systems design

Urban water reuse is a term generally applied to the use of reclaimed water for the beneficial irrigation of areas that are intended to be accessible to the public, such as golf courses, residential & commercial landscaping, parks, athletic fields, roadway medians, etc.

Expanded uses for reclaimed water may also include fire protection, aesthetic purposes (landscape impoundments and fountains), industrial uses and some agricultural irrigation.

Reclaimed water is domestic wastewater or a combination of domestic and industrial wastewater that has been treated to stringent effluent limitations such that the reclaimed water is suitable for use in areas of unrestricted public access. Since most areas where reclaimed water is to be used are designated for public access, protection of public health is the primary concern. Although utilization of reclaimed water will be beneficial, there is no guarantee that this source will provide all the water that is needed or desired.

Highly treated reclaimed water that meets the requirements of these guidelines is a valuable water resource. Wastewater treated to urban water reuse standards may be used in lieu of potable water for agricultural irrigation (feed crops), residential/commercial landscape irrigation, dust control, etc. The reclaimed water system is an integral part of the utility system and provides benefits to both the potable water and wastewater utilities.

Some of the substances that can be removed from wastewater include:

  • Suspended solids
  • Volatile organics
  • Semi-volatile organics
  • Oil and grease
  • Hydrocarbons
  • Metals
  • BOD
  • COD
  • Color
  • Odor
  • Hardness
  • Minerals

Reclamation processes:

Wastewater must pass through numerous systems before being returned to the environment. Here is a partial listing from one particular plant system:

  • Barscreens – Barscreens remove large solids that are sent into a grinder. All solids are then dumped into a sewer pipe at a Treatment Plant.
  • Primary Settling Tanks – Readily settable and floatable solids are removed from the wastewater. These solids are skimmed from the top and bottom of the tanks and sent to the Treatment Plant where it’ll be turned into fertilizer.
  • Biological Treatment – The wastewater is cleaned through a biological treatment method that uses microorganisms, bacteria which digest the sludge and reduce the nutrient content. Air bubbles up to keep the organisms suspended and to supply oxygen to the aerobic bacteria so they can metabolize the food, convert it to energy, CO2, and water, and reproduce more microorganisms. This helps to remove ammonia also through nitrification.
  • Secondary Settling Tanks – The force of the flow slows down as sewage enters these tanks, allowing the microorganisms to settle to the bottom. As they settle, other small particles suspended in the water are picked up, leaving behind clear wastewater. Some of the microorganisms that settle to the bottom are returned to the system to be used again.
  • Tertiary Treatment – Deep-bed, single-media, gravity sand filters receive water from the secondary basins and filter out the remaining solids. As this is the final process to remove solids, the water in these filters is almost completely clear.
  • Chlorine Contact Tanks – Three chlorine contact tanks disinfect the water to decrease the risks associated with discharging wastewater containing human pathogens. This step protects the quality of the waters that receive the wastewater discharge.

At various stages in the multistage treatment process, unwanted constituents are separated using

  • Vacuum or pressure filtration,
  • Centrifugation,
  • Membrane-based separation,
  • Distillation,
  • Carbon-based and zeolite-based adsorption, and
  • Advanced oxidation treatments.

Activated carbon is a highly adsorbent form of carbon that is produced when charcoal is heated. It removes impurities via adsorption from both aqueous and gaseous waste.

Membranes allow materials of a certain size or smaller to pass through but block the passage of larger materials. Imaginative arrays of membrane materials in innovative physical configurations are used to separate unwanted solids and dissolved chemicals from tainted water. During operation, purified water diffuses through the micro-porous membranes and collects on one side of the membrane, while impurities are captured and concentrated on the other side.

Today, membranes made from cellulose acetate, ceramics, and polymers are widely used. The applications come in a variety of innovative designs, including tubular, hollow-fiber, plate-and-frame, and spiral-wound configurations. The goals of membrane design are to

  • Maximize the available surface area,
  • Reduce membrane pore size (to allow for the more precise removal of smaller contaminants),
  • Minimize the pressure drop the fluid will experience when flowing through the unit, and
  • Identify more cost-effective system designs.

The addition of oxidizing agents—chemical ions that accept electrons—has proven effective against these microorganisms like waterborne viruses, bacteria, and intestinal protozoa. Today, a variety of advanced oxidation techniques kill such disease agents and disinfect water, thanks to ongoing developments pioneered by the chemical engineering community.

Historically, chlorine-based oxidation has been the most widely used, and it is very effective. However, the transportation, storage, and use of chlorine (which is highly toxic) present significant potential health and safety risks during water-treatment operations. To address these concerns chemical engineers and others have developed a variety of alternative oxidation treatments that are inherently safer, and in many cases more effective, than chlorination. These include Ultraviolet light,Hydrogen peroxide, and Ozone, each of these powerful oxidizing agents destroys unwanted organic contaminants and disinfects the treated water without the risks associated with chlorine use.

Considerations for constructing a water reclamation system:

In planning for urban reuse there are three major issues that must be considered prior to developing such a system.
The first issue is that year round wastewater treatment and disposal are required when designing any wastewater treatment facility. A water balance for the reclaimed water service area is needed to determine how much wastewater will be generated and how much irrigation demand there is for the reclaimed water. The wastewater generated may exceed the reclaimed water demand during portions of any given year. Therefore, a discharge permit, additional storage, or a designated land application site may be required.

The second issue which must be considered is the constituents (e.g. salts) that may be present in the reclaimed water and what effect(s) they may have on the cover crops that will be irrigated. For specialized users such as golf courses, nurseries, etc., a detailed evaluation of the effluent constituents may be necessary in order to determine whether or not they are candidates for urban reuse irrigation.

Third, Urban Water Reuse is not suitable for all wastewater treatment applications. The manpower requirements and permit reporting can make a reuse facility expensive for a small operation. The facility’s operator in responsible charge shall be a Class I Biological Wastewater Operator. Operation of reclaimed water systems requires on-site operation by a Class II Biological Wastewater Operator or higher operator 8 hours per day, 7 days per week. If the operator can monitor from a remote location and receive immediate notification for alarms, a reduced schedule for on-site operation by a Class II Biological Wastewater Operator or higher operator may be considered on a case-by-case basis.

Deciding how best to use wastewater begins with a laboratory analysis of the substances present in the water. Engineers work with each client to specify the laboratory tests that should be performed. Once that information has been obtained, our engineers and the client:

  • Identify the various ways the water can be used in the specific facility
  • Identify the substances to be removed from the water to make it suitable for each use
  • Determine the process needed to re-condition the wastewater for each use
  • Estimate how much water consumption would be saved by recycling and calculate the annual cost of the water
  • Obtain a cost estimate for the required treatment system
  • Compare the cost savings of reduced water consumption to the capital and operating expenses of the treatment system to determine whether the investment in recycling is cost-effective

Why wait? Start building your water reclamation systems design from the best water reclamation design companies now; get help & assistance from the top highly skilled & technical experts.