WASTEWATER DEVELOPMENTS: PHOSPHORUS
By Pat Kneip, P.E.
Most industries that discharge process wastewater to a Publicly Owned Treatment Works (POTW) have not had to worry about phosphorus compliance. Unfortunately, this pollutant needs to be put on the radar screen of environmental, health and safety (EHS) managers, since increasing phosphorus scrutiny at the federal and state level is starting to trickle down to POTWs. As a result, some industries are starting to see phosphorus limits in their wastewater discharge permit renewals, while others will likely be seeing them soon. This is a big concern for many industries, since this pollutant is present in many raw materials and products at levels above likely discharge limits. To make matters worse, there are no simple and inexpensive forms of pretreatment.
Phosphorus has been a concern from a regulatory standpoint because of the eutrophication of surface waters and the difficulty in controlling contributions from non-point sources (i.e., agriculture). The U.S. Environmental Protection Agency (EPA) and many states have already begun tomore stringently regulate phosphorus through permitting for direct dischargers (including POTWs) under the National Pollutant Discharge Elimination System (NPDES). Some states are implementing regulatory changes that would decrease phosphorus limits by as much as 90 percent, which would require expensive upgrades to many POTWs. As the POTWs become more stringently regulated with regard to phosphorus, they have no choice but to pass along those restrictions to industrial dischargers.
Phosphorus is present in process wastewater discharges from a wide variety of industrial categories, including steel production, metal finishing, food and beverage processing, industrial cleaning, pharmaceuticals, and of course fertilizer production. While discharge levels in some industries may be relatively low (i.e., 50 to 100 mg/L, POTWs are developing permit limits below 20 mg/L in some cases. Limits this low will obviously be problematic for heavier industries, but many lighter industries, including food and beverage processing, will also struggle. For example, facilities that process/produce baked goods, meats, dairy products, soda, and beer all have the potential for compliance challenges due to the phosphorus contained in raw materials, finished products, and cleaning/sanitizing chemicals. Process cleaning and sanitation activities (i.e., Clean In Place/Clean Out of Place) result in the discharge of elevated levels of phosphorus to the POTW.
While phosphorus removal can be accomplished chemically, biologically, or physically, it can’t be done quickly, easily, or inexpensively. Chemical pretreatment typically involves the use of a coagulant (alum, calcium hydroxide, or ferric chloride) and clarification with a high sludge generation rate. Capital costs are moderate, but operating costs can be high. Biological pretreatment is possible through several different processes, yet capital and operating costs are very high and so are the space requirements. Physical pretreatment, beyond clarification, involves filtration through different media options and sometimes in combination with chemical approaches. Some of these options are moderate in terms of cost but can also be only moderate in terms of removal efficiency. Membranes are the most effective means for phosphorus removal and can be combined with biological processes (i.e., membrane bio-reactors), but capital and operating costs are very high. How much pretreatment may cost depends entirely on how much phosphorus needs to be removed and how much can be taken out through proactive options like waste minimization, production recovery, and beneficial reuse.
PSARA recommends the following steps to stay ahead of this developing issue:
Pretreatment projects can take up to a year for planning, capital approval, regulatory approval, design, installation, and startup/shakedown, so stay ahead of the game!To find out more about this topic, click here.