Core Services - Overview
CleanEarth offers a menu of services, features and benefits from which you can choose to meet your ultimate wastewater objectives.
Each company's order of priorities is unique, but we've found that the above "wish list" combines most of what people are looking for. If you have other needs, let us know and we'll see what we can do!
The Basics - Heavy Metal Ion Removal
One of the easiest ways to remove heavy metal ions from wastewater is to bombard them with a lot of iron, calcium, aluminum and other non-regulated metal ions. This electrochemical saturation attracts whatever the heavy metal ions are attached to that is allowing them to stay dissolved -- typically chloride or sulfate ions. The heavy metal ions are then freed up to combine with hydroxide and other chemicals and fall out as sludge.
Even though adding metal ions is one of the easiest ways of treatment, it is also quite expensive. Chemicals, labor and sludge are the requisites of conventional chemical precipitation. And, our experience has taught us that 80%-90% of chemicals consumed are used to remove the last 5%-10% of heavy metal ions.
Another problem -- and it's a difficult and costly one -- is chelation. Chelation is a phenomenon whereby a chelator (typically EDTA, ammonia or a hydrocarbon) wraps around a metal ion and won't let it go. It either smothers it with electrons so that nothing can compete with it, or it binds with it in a solid form (microscopic sludge) and insulates it from exposure to chemical treatment.
If, no matter how much chemical is used, you still can't get the metal ions down to undetectable levels, there's some chelation present.
O.K., so what's the answer to reducing chemicals and sludge?
Well, the obvious approach is to replace the chemicals with something that does the same job, but is not consumed in the process and does not add to the amount of sludge produced.
There are a number of technologies that fall within this broad criteria. Electrofloculation, ion-exchange and electrolysis are a few of the best known.
Our experience has shown that ion-specific, ion-exchange resins provide the most efficient removal of heavy metal ions when the system is properly designed.
By using ion-exchange resin, the bead (which is loaded with sodium or hydrogen ions) exchanges the sodium or hydrogen for an ion with a higher molecular weight.
When the resin becomes loaded, it is rinsed with acid to strip the metal ions. This step is called elution and the acid/metal solution is call eluent. Then, in some cases, the resin is re-conditioned with caustic to load sodium on the beads. The eluent is recycled back to the beginning of the system where it is neutralized and the metal falls out as sludge.
This process minimizes -- and most the time eliminates -- the need for precipitation chemicals such as iron, aluminum, magnesium, polymers and the worst of all, carbamate.
The Basics - Reducing/Re-using Process Water
Plating facilities we've audited fall into three categories -- misers, diluters and the ones who use about the right amount of water.
We've seen thousand gallon tanks sitting stagnant and 300 gallon tanks with 40 gpm flow-through (no kidding).
For the most part, we've seen platers wanting to reduce the amount of water they buy and discharge, yet they need at least the same amount of water they now use to rinse parts.
That requires some type of recycling technology that will separate contaminants -- mainly dissolved solids -- and allow the re-use of a majority of the water.
The most efficient process for recycling water uses membrane technology to separate the contaminants from the water. Ultrafiltration, nanofiltration and reverse osmosis all use specially-prepared membranes that operate under pressure and allow water to pass through while rejecting larger molecules and negatively charged ions.
One technical hazard of using membrane technology is that the performance models for flows, costs and life are all based on processing city water or ocean water, not greasy wastewater containing strong oxidizers that absolutely destroy the membrane surfaces. No membrane manufacturer will warrant the performance of its products in a wastewater environment. Plus, all the information about flux (water passage) and life just don't apply. If you ever decide to use this type of technology, contract for a specific amount of water and a certain quality of water. Otherwise, if your system designer uses the manufacturers' model, the system will be half the size needed and contain the wrong membranes.
That's the bad news. The good news is that membrane technology does work and produces water quality better than the city water you are using now. And the economics work as well. When everything is considered -- labor, equipment, water/sewer costs, chemicals, sludge -- a 75% recycle rate can break even.
And keep in mind that at 75%, you only have to treat 25% as much water. This provides a great benefit to those who are at, or are approaching, capacity in wastewater treatment.
Membrane technology has improved a lot in the last five years. Membranes are now made which can recycle acid, caustic, oxidizers (hex-chrome) and other special applications like organics (triethanolamine, corn syrup, orange juice, milk, etc).
The most important consideration in designing a membrane system is the filtration available before the membranes. Membranes are made only to separate dissolved solids from water -- things like salts and low levels of acids and hydroxides. Any sludge, silica, bacteria, algae or other non-dissolved, solid particles will block passage of water and render the membrane useless. Once the membrane is fouled in this manner, it is impossible to clean.
We toured a facility last year that had a 13 mgpd (million gallon per day) reverse osmosis system. Their 15 million gallon storage tank, which was open to the elements, was filled about two weeks before the system was ready for the ribbon cutting ceremony (municipal system). Once the system was turned on, over half the membranes were irreversibly fouled within two days by algae that had grown in the stagnant storage tank.
At a flux rate of 2400 gpd per membrane and a cost of $1,200 each, that was a multi-million dollar mistake. This could have been averted with the proper pre-filtration and disinfection hardware upfront. Or least some type of detection device for turbidity, delta pressure or SOMETHING!
Just remember that there is no such thing as too much pre-filtration in a membrane system.
So, to summarize the primary technologies, the best way to reduce sludge is by using ion-exchange to replace precipitation chemicals. The best way to recycle water is to use a membrane system which will economically produce 75%-80% good water from your wastewater stream.