ARTICLE
Rare earth coagulant helps Hartford, WI achieve stringent phosphorus limit of 0.075mg/L
When the state of Wisconsin created stringent new water quality standards in 2013 to protect surface waters from eutrophication, about 400 treatment plants received tough new discharge limits for total phosphorus, ranging between 0.5 and 0.04 mg/L.
Though many of the treatment plants already had chemical phosphorus removal systems in place, the Wisconsin Department of Natural Resources (WDNR) estimated that most would not be able to comply with the new standard without additional equipment such as biological phosphorus removal, sand filtration, rapid mix and flocculation chemical removal or others. Chemical coagulation alone, it was assumed, would not be able to achieve the low phosphorus limit.
One plant, the City of Hartford Water Pollution Control Facility (HWPCF), decided to try Neo rare earth coagulant to see if the chemical could enable it to achieve a new, ultra-low phosphorus discharge permit of 0.075 mg/L. If it worked, the plant would likely be able to avoid spending $2.8 million for new nutrient removal equipment, along with higher annual maintenance and operating costs that would accompany that approach.
HWPCF switched its ferrous chloride coagulant with Neo RE100, and within a three-week equilibration time was able to consistently maintain average total phosphorus in treated effluent from an average influent level of 7.3 mg/L to an average of 0.072 mg/L in final effluent. This was a remarkable achievement since attempts to reach 0.075 mg/L with ferrous chloride were unsuccessful. Even ferrous chloride doses as high as 120 ppm could only reduce phosphorus in final effluent to 0.3 mg/L.
Cold-weather testing with Neo RE100 was also very successful. A study from December to March showed that the rare earth coagulant could consistently reduce average total phosphorus to 0.036 mg/L in final effluent.
Neo RE100 and RE300 are able to achieve this high level of phosphorus removal because it incorporates rare earth elements Cerium and Lanthanum that bind tightly to phosphorus and form a dense precipitate that readily settles out of solution within minutes.
Since switching to Neo RE100, the plant has also experienced better sludge settling, a 35% reduction in solids production and reduced odour in the non-potable water system.
