York City's 275th Anniversary

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Ask the Operator

This page will be devoted to answering questions that you may have concerning our processes. If you have other questions that you would like us to address, please email us at carnold@yorkcity.org.

How many operators do you currently employee to run your operation?

We staff our facility twenty-four hours per day all year round. At the present time we have one Process Control Manager, three Shift Supervisors, nine Plant Operator II, one Plant Operator I, and four Filter Dryer Operators.

We operate on fixed 8 hour shifts. Each operator then has two consecutive days off for his weekend.

What steps do you take to ensure that your personnel are kept adequately trained and informed?
  • We provide training sessions on various treatment processes and equipment throughout the year. This training is scheduled so that all operators get the same information.

  • We have developed Standard Operating Procedures. These are kept in our Computer Room and are available to all personnel. The procedures are referred by an operator who is working in an area or classification that he is not entirely familiar. The S.O.P.s cover subjects like sampling schedules, staffing requirements, overtime procedures, equipment inspections, and various process operations.

  • Since our plant is extensively computerized, we felt the need for a computer graphic handbook. This document explains all the various computer graphics. It can guide an operator through an unfamiliar graphic procedure.

  • Documentation on our Co-Generation system is also available to the plant operators. It is also kept in the Computer Room. While this system remains highly automated, there are procedures to be followed in the case of a power outage or generator malfunction.

  • Each week the Process Control Manager issues a "Weekly Memorandum". In it he documents the activities of the past week. This lets the operators know what changes occurred over the past seven days.

The phosphate concentrations in our biological process effluent rises on weekends and then drops off again during the week. What is causing these fluctuations?

Our experience has been that this is caused by a lack of soluble B.O.D. over the weekends. The biological process for phosphate removal is very dependent on how much soluble B.O.D. is entering the anaerobic phase. We have found that when the soluble B.O.D. drops below 30 mg/l, we can expect an increase in the phosphate levels.

One way you can counteract this problem is to reduce your return rate. This would lower your MLSS and increase your F:M ratio.

I have a fluffy white foam on my aeration tanks. What is causing this foam?

A white fluffy foam usually is indicating a young mixed liquor. An observation of the mixed liquor under the microscope should confirm this based on what indicator organisms are present. A reduction in the wasting rate may be necessary.

At what temperature should I keep my anaerobic digester?

This depends on your operating parameters. Here at York we operate our digesters in the mesophilic range. Our computer system monitors the temperature of the digester contents. If the temperature drops below 98 degrees F., then the computer turns on the hot water recirculation pump to heat up the sludge as it flows through the heat exchanger. When the temperature in the digester goes above 99 degrees F., then the computer will turn the hot water recirculation pump off. As you can see we operate on a very tight temperature variation. This adds to the stability of the process.

At what level do you keep your primary clarifier sludge blanket?

Our goal here is to keep the sludge from going septic in the primary clarifiers. We want the anaerobic breakdown to occur in the digesters where the gas can be collected and used in our Co-gen facility. We have found that we must keep our sludge blanket levels around the 1 foot level. Above 2 feet and septic conditions develop. When blankets are less than 1/2 foot, we send a "thin" sludge into the digesters.

What has been your experience with ultraviolet disinfection? Our facility is considering using this system versus Chlorination?

We have had excellent results with our UV system. Typically our fecal counts are less than 4 colonies/100 mls. Cost studies have shown that the UV system has been more economical than that of Chlorine. Also, while there are some safety concerns with the UV system, they are far less serious than that of Chlorine.

The lamps in our system have an automatic wiping system that keeps them clean. Having shallow bed sand filters upstream of this system has helped in keeping the bulbs clean.

What biological processes are at work in an anaerobic digester and how can I insure proper operation?

First there are two different groups of bacteria responsible for anaerobic digestion. They are "ACID FORMERS" & "GAS FORMERS".

The Acid Formers breakdown complex organic matter into volatile acids. The acid formation occurs in the first phase of anaerobic treatment.

The Gas Formers breakdown this organic acid and produce methane gas and carbon dioxide.

The growth of these bacteria are selected for by the existing anaerobic(no elemental Oxygen)conditions.

One thing to keep in mind is the delicate balance is needed to keep both Acid Formers and Gas Formers in check. We do this by monitoring both the concentration of volatile acid and alkalinity in the digesters. If the pH drops below 6.5 std. units(do to high production of acid), gas production would drop off due to the toxic effect of the low pH on the Gas Formers.

You stated that you generate over 2.5 million kw of electric power per year. On an average day, how how much electricity do you purchase from your utility?

On average, we purchase 20,000 to 22,000 kw per day from our electric utility.

Our wastewater treatment plant has a problem with grease build up in our primary clarifiers suction and discharge lines. We have tried various chemicals and enzymes with little success. Do you have a similar problem and what action have you taken?

Yes, we have experienced the same problem here and have gone through the chemical and enzyme routine. We then found that hot water works extremely well and have designed and installed a system that has virtually eliminated this problem. Pumping rates have gone from 80 gpm to 170 gpm with two treatments.

It is also important to size the primary sludge pumps so that an adequate velocity can be maintained to keep the pipes scoured. Just recently we modified our primary sludge pumps to increase their pumping capacity. After doing this we were able to reduce the number of times that hot water had to be used to melt away any grease deposits.

Do you have to scrub the methane gas your digesters produce prior to using it in the Co-generation system?

No. We don't have to scrub the gas. We test it quarterly and have had no problem with it in our generation system. Typically, our Hydrogen Sulfide concentrations are less than 0.1%.