Clean-water plants are challenged to meet ever-stricter limits on effluent phosphorus.

Typically, the remedies include chemical treatment, media filtration and process changes enabling biological removal, or some combination of these. A major difficulty is cost, especially for smaller facilities with constrained budgets.

Bishop Water Technologies and Neo Chemicals and Oxides offer a phosphorus removal alternative in the U.S. and Canada through distributors such as WaterSolve. It comes in the form of a rare-earth-based coagulant that they say can help plants cost-effectively achieve effluent phosphorus as low as 0.07 mg/L without tertiary filtration. 

The coagulant, Neo RE300, has the rare-earth elements lanthanum and cerium as the active ingredients. It is designed to replace conventional ferric- or alum-based coagulants. Its rare-earth minerals bond tightly to phosphorus to form a dense, heavy precipitate that settles about twice as fast as with conventional chemicals, improving clarifier performance while reducing the amount of coagulant used and the volume of solids produced. 

The material also inhibits the formation of struvite and, being rated as nonhazardous, is safe for operators to handle. Kevin Bossy, CEO of Bishop Water Technologies, and Marc Rancourt, wastewater specialist, talked about the offering in an interview with Treatment Plant Operator.

TPO: What was the rationale for bringing this product to market?

Bossy: Our BioCord reactors were developed for ammonia removal, and we wanted something that would complement that as it pertained to phosphorus removal. We found the RE300 product to really work well, giving us a complete nutrient removal solution for both ammonia and phosphorus.

TPO: In simple terms, how does this product work as compared to conventional additives like ferric or alum?

Rancourt: An easy way to think about it is in terms of the strength of the bond. The reaction of phosphorous and the RE300 elements is analogous to a strong Velcro bond, whereas with the legacy chemistries, it’s more like the static electricity bond you get from rubbing two balloons together. It also works at a lower dosage. Typically, for example, alum reacts on a 5:2 ratio — five parts alum to two parts phosphorus. With RE300, it’s a one-to-one molar ratio. That means less dosage to get a better result.

TPO: Are there any other benefits from the rare-earth coagulant?

Rancourt: There are trickle effects downstream. For one, less dosage means less sludge production. Testing has also shown that the sludge dewaters more readily, yielding a drier material. That means less transport of sludge so lower greenhouse gas emissions. It’s also a safer product. It’s less acidic so there is less corrosion of plant infrastructure. In addition, it can be stored outside down to 40 degrees F below zero. That means in many cases there is no need for an energy-consuming heat trace on lines feeding it into the process.

TPO: Where in the process would this product be added for the greatest effect?

Rancourt: Every treatment system is a little bit different. It’s about knowing the dynamics of the system. Where do you have the most retention time, and where is the best opportunity for success in a particular system? At the front end of the system, in the primary clarifiers, is probably the most common site for injection. Getting most of the solids out before you add it is key. If you add it where there are a lot of suspended solids, you will consume some of the coagulant unnecessarily. But every setup is a little bit different. 

TPO: What does this material look like?

Bossy: It’s a clear liquid, a concentrated solution. We sell it in totes like any other liquid chemistry. It is also available in tankers.

TPO: Is any special kind of feed system needed for this product?

Bossy: If you’re already using an inorganic coagulant, there is nothing you need to change. You would use the exact same feed system.

TPO: What about mixing systems?

Rancourt: It’s no different from any other chemistry. You need it to be well distributed to get good contact with the phosphorus, but there are no special mixing requirements.

TPO: Does your company offer any services to help customers find the optimum dosage?

Rancourt: Bench testing is always the first step. We use a calculator to determine the optimum feed rate. We don’t just look at parts per million. We can target specifically down to the molar ratio. It helps to have an analysis on the different fractions of phosphorus, meaning what portion is soluble versus insoluble, reactive versus nonreactive. That can help us target the dosage better.

Bossy: We also fabricate our own line of chemical feed equipment. We are there for customers, come what may. If they don’t have the feed equipment, we can provide that.

TPO: What makes this material more cost-effective than conventional chemistries?

Bossy: It’s less expensive on life-cycle cost. When you look at the absence of heat tracing, the better dewatered solids, the less sludge produced, and the avoidance of capital equipment associated with filters if you have particularly low limits, that’s where it’s cheaper.

TPO: What results have facilities seen in using this product?

Rancourt: First and foremost is consistently meeting ultralow phosphorus limits. There is no doubt the product works. It will get you to levels of phosphorus as low as 0.07 mg/L. In addition, a 25% to 30% reduction in sludge volume is not uncommon.

TPO: Are there any sizes of plants for which this product is most advantageous or any other kind of sweet spot?

Bossy: The size of the plant doesn’t matter. What matters is the total phosphorus limit. If you don’t have a total phosphorus limit, this isn’t a product for you. If your limit is 1 mg/L, then traditional coagulants may well be a better option. Once you’re at a 0.5 mg/L total phosphorus limit, that’s the sweet spot for RE300.