Improving Compliance Through Real-Time Phosphorus Control

Real-time control offers continuous monitoring to allow accurate dosing, giving plants better control over operations, regulatory compliance and costs

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Improving Compliance Through Real-Time Phosphorus Control

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Phosphorus is essential to life and so it is present in plants and animals. Phosphorus promotes growth, which is good for a fertilizer, but bad for wastewater effluent.

When phosphorus is discharged in wastewater from beverage, food and dairy processing plants, usually in the form of PO4, it “fertilizes” algae and aquatic plants so they multiply and deplete the oxygen in streams, rivers and bays, ultimately choking out larger organisms and disrupting the healthy balance of the ecosystem.

Regulations exist to protect water, wildlife and people from uncontrolled amounts of phosphorus in wastewater, and these regulations have an economic impact on beverage, food and dairy processors. There are costs associated with removing phosphorus from wastewater, but there are higher costs associated with failing to remove it adequately or reliably. Most immediate are fines levied by state and EPA regulators for high-profile events like fish kills or algae blooms that impact community water sources. Most lasting are the impacts on the reputation of the beverage or food processor as an employer and brand.

Clearly, phosphorus must be controlled and discharge limited to safe levels.

Manual monitoring, manual dosing

Wastewater from beverage, food or dairy processing plants usually goes one of two places: directly back into a natural waterway, or to a municipal wastewater treatment plant for further treatment. Permits and regulations vary between the two, and the upper limit for phosphorus depends on location as well.

Traditionally, regulatory agencies test for phosphorus by setting up a water sampler downstream from a processing plant and taking samples at set intervals; for example, once per hour. Then this composite sample is tested once a day, and if it exceeds the permitted level of phosphorus, the agency levies a fine. In order to avoid fines, plant operators test their own effluent periodically. The more often they can draw samples, the more accurately they can measure phosphorus over time and dose control agents more precisely. However, the labor cost of manual sampling is multiplied as the number of samples increases, so most sites choose a testing interval and hope that it’s frequent enough to detect changes. To compensate, the sites overdose with FeCl3 to provide a safety margin.

The result of this approach is that sites often use too much or too little chemical and that is when they get fined. If, for example, their allowable limit is 1.0 mg/L, a site may set their dosing levels to achieve 0.8 mg/L based on the average phosphorus content of their effluent, hoping this will be sufficient to control variations. The intent is to reduce risk and uncertainty, but this does not really improve controllability. This strategy uses 20 percent too much ferric chloride most of the time, while not controlling sudden phosphorus spikes. Spikes can occur for various reasons. A process changeover or increase in process speed increases water flow, discharging more phosphorus. Cleaning operations might use phosphate-containing detergents and high-pressure, high-temperature water that can suddenly send higher than average amounts of phosphorus downstream. In short, plant operators are hit with costs two ways: paying too much for dosing chemicals while still being fined for excess phosphorus.

Real-time control

Increasing frequency of grab sampling improves the chances of detecting changes in phosphorus levels, but these grab samples only provide a snapshot of stream conditions. Dosing rates are based on composites of grab samples over a previous time period, so operators are dosing for past discharges, not the current one.

Fortunately, there is proven technology for automating real-time monitoring and dosing control that can give beverage, food and dairy plant operators the data and control they need to meet regulations without overspending on chemicals. A system of compatible, integrated sample analyzers and dosing controllers all managed from a central control unit takes the guesswork and human error out of phosphorus treatment.

A complete, integrated real-time control system starts with automatic analyzers. The Phosphax sc Digital Phosphate Analyzer from Hach can prepare and analyze a sample in under five minutes. Set in a ruggedized weatherproof housing it can be set right at the tank to provide continual, highly precise measurements of phosphorus levels with detection limits as low as 0.05 mg/L. It is designed to use minimal amounts of reagent. Multiple output options are available, making it easily compatible with existing systems.

The analyzer sends data to a central controller, the Hach SC1000 Multi-Parameter Universal Controller. This solid-state, modular controller can monitor up to eight sensors directly or be networked to monitor 32 sensors, each analyzing different parameters. A large color touch screen lets operators observe system status quickly. Parameters can be adjusted easily when processes change.

The central controller receives data from the analyzer and sends commands to a Phosphorus Real-Time Controller (RTC-P) that manages the coagulant (typically FeCl3) dosage in real time. It signals the feed pump to discharge the appropriate amount into the effluent stream.

The Hach RTC-P also includes PROGNOSYS software for predictive diagnostics. This subsystem continually monitors the RTC-P system and delivers status alerts so operators can take proactive troubleshooting, maintenance and repair action.

Benefits of real-time control

The main benefit of using real-time control to monitor phosphorus is maintaining compliance with permits thanks to more accurate chemical dosing. Being able to control changing phosphorus levels, even when the concentration fluctuates widely and unexpectedly, reduces risk and variability in effluent discharge.

One dairy plant was able to maintain phosphorus compliance without overdosing ferric chloride. This had the added benefit of reducing dosing by an average of 33 percent, saving $1,863 per month. A soft drinks manufacturer was also able to meet its compliance limits. Their phosphate discharge values are now controlled at less than 2 parts per million total phosphorus. Total suspended solids and turbidity readings are also reduced by approximately 10 percent.

Other savings come from reducing labor costs associated with manual sampling and coagulant pump setting changes. Also, more accurate dosing reduces sludge creation.

Additional benefits come from using a prepackaged, turnkey integrated system composed of proven components. In contrast with house-built solutions that string together various pieces, a turnkey system saves staff resources and time while building on its expertise. It ensures continuity of institutional support rather than relying on one person or a department that will eventually turn over. It also ensures the interoperability and optimization of the components and software. An automated RTC-P system helps plants reduce operational complexity.

In short, automated real-time phosphorus control reduces variability and makes outcomes more predictable and controllable. This is better for both the environment and the bottom line.

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