The two surface water treatment plants, Oradell and Haworth, have a nominal capacity of 80 and 25 mgd, respectively, and a peaking capacity of 110 and 50 mgd, respectively. Ultimate demand projections for our current service area indicate an average daily flow of 165 mgd, peaking at 240 mgd. -

The Oradell Plant was initially constructed in 1904, with additions in 1913 and 1955. The Haworth Plant was completed in 1964. The Oradell Plant served well, being modified during those years to meet treatment and pumping needs. However, it was beginning to approach its expected life and major rehabilitation was needed. There was a need to begin thinking of expansion and new construction, always keeping in mind present and potential future water quality regulations.

In 1979, the Hackensack Water Company was in the midst of a dilemma. The Oradell Plant was quickly approaching its useful life. Additional capacity was needed. The concern over future water quality regulations was deep in our thoughts, especially those for trihalomethanes. Our initial concept was to enlarge the Haworth Plant from 50 to 100 mgd and rehabilitate the Oradell Plant to provide 100 mgd using conventional treatment. However, our concern over trihalomethanes, as well as our consultant's concern, prompted us to look at alternative oxidants/ disinfectants.

In 1980, our consulting engineers, Buck, Seifert and Jost, Inc., designed a proto-type pilot plant using ozone as the primary oxidant/disinfectant in conjunction with direct filtration. Hackensack Water Company spent the next four years piloting the use of ozone. The pilot plant went through several modifications studying the different aspects of ozone in water treatment and potential plant design. In the end, based upon this pilot study, the final plant design was authorized incorporating criteria for air preparation, capacity and number of ozone generators, size and configuration of contactors, means of gas diffusion, vent gas handling, flotation of solids, filter design and media sizing, backwash procedure and down to the final residual disinfectant.

But most astonishing, because of the use of flotation and direct filtration, the Haworth Plant could now be quadrupled to 200 mgd, eliminating the need to rehabilitate the original plant and at a capital and operating cost no greater than that of conventional treatment.

After four years of exhaustive pilot plant studies, design criteria were established which were used as a basis of design for the Haworth Treatment Plant expansion. These criteria are shown in Table No. 1.

Alum = 7.5 mg/L Rate = 6 gpm/sf

Cationic Polymer = 1.5 mg/L Anthracite = 27" of 1.5 mm

Ozone = 1.3 mg/L Sand = 12" of 0.60 mm

Ammonia = 0.4 mg/L Gravel = 6" of 3/8 x 3/16 in.

Chlorine = 2.5 ma/L Backwash = combination air/water

Due to the importance and the complexity of the ozonation equipment, a joint decision was made by the water company and the consulting engineer to prepare a performance specification for purchase of the ozone equipment. Not only did the contract provide for penalties for failure to meet the specifications, but also included maintenance and operational assistance for a period of two years after acceptance of the equipment. The contract for the ozonation equipment was awarded in April of 1984, thus allowing the final design of the Ozone Building and the Ozone

Contactors to be based on the actual equipment being furnished.

The design of the full plant expansion was completed in early 1985 and the general construction contract awarded in May of 1985. Actual construction began in June of 1985 with completion, including modifications to the existing facilities, expected in the second quarter of 1990.

The new facilities consist of an ozone building, ozone contactors, and a combined -facility consisting of the filters; process control and administrative and training facilities; and the filtered water pumping station. This combined facility has been built adjacent to the existing filter building to allow for easy interconnecting between the new and existing structures. In addition to the new construction mentioned, a new dual feed substation was constructed along with standby power facilities.

The first floor of the Ozone Building houses the alum and polymer storage tanks and feed equipment along with the Air Preparation Room for the ozone generation facilities. Within the Air Preparation Room are the air filters, air compressors, refrigerant driers and desiccant driers. The equipment is designed to reduce the incoming ambient air to a dew point of -76°F (-60°C).

The second floor contains the high voltage low frequency ozone generators, along with the computerized control panels for the four (4) individual ozone generation trains. Each train is designed to provide a maximum of 675 lbs/day of ozone for a peak of 55 mgd of water.

The four (4) Ozone Contactors are 55'x55'x26'(SWD) reinforced concrete structures. The design brings the chemically treated raw water into the circular center column which houses the turbine type ozone diffuser. At nominal flows, the detention time in the center column is 2 minutes with a total detention time of 21 minutes for the whole contactor. A minimum of 92% transfer efficiency is guaranteed.

The results of the pilot studies showed a tendency of the solids to float, the flocculating compartments of the existing coagulation basins were converted to flotation skimmers with the existing sedimentation compartments acting as flow through conduits. It is expected that 20% of the solids generated can be removed by flotation. After the water is skimmed it is filtered through twelve (12) new and eight (8) existing renovated dual media filters. The surface area of each filter is 1144 sf. They are constructed of pre-cast concrete bottoms with approximately 6000 high impact plastic filter nozzles. Each filter can filter at a rate of up to 10 mgd.

As stated earlier, standby power facilities have been constructed with the plant expansion. These facilities consist of two (2) 4000 KW gas turbine generating units along with the necessary control building and fuel storage tanks. These units are sized to provide a minimum of 60 mgd to the system in the event of a power failure. These facilities have also been designed to allow us to load share on request from the power company.

The treatment plant process is controlled by a distributed processing computer system. The system consists of ten (10) data processing and control computers which perform specific assigned functions within the process. They communicate with each other through a common data highway. The plant operator can control and monitor the plant process through a video console in the Plant Control Room. The plant can also be operated manually at each local control panel. The plant operating records are continually saved on tapes and can be retrieved for reporting and data analysis.

The plant output is dictated by the distribution system pressure which is preset within a prescribed operating range. The output pressure is trimmed via the finished water discharge valves. The raw water input is set at a rate to maintain a static operating level in the retention basins. If the system pressure falls or rises outside the operating range, the computer will alert the operator to start or stop a pump. The reason for the human intervention is to avoid unnecessary start/stop of pumps when certain demand peaks and valleys are anticipated.

Since each ozonation train can process 55 mgd, not all four (4) trains will be in full-time operation. One or two of the trains will be on standby. When the computer detects a change in the need for a train, it will again alert the operator. For the same reason, as that of the finished water output pressure, human intervention will give final approval for a change in the number of ozone trains.

The ozone dosage is controlled by the ozone concentration in the off-gas discharged from the top of the ozone contactors. The information on the off-gas ozone is fed to the ozone generator controls which in turn adjusts the applied voltage to vary the ozone produced.

Alum is used as a primary coagulant. A low molecular weight cationic polymer is used as a coagulant aid. They are applied in succession at the influent channel of the ozone contactors. The early addition of the coagulants enhances the micro-flocculation effects of ozone in the contactor and allows the contactor to be used as a complete mix reaction vessel. The coagulant dosage control is based on the finished water turbidity, and the raw water color and turbidity.

In order to remove the last trace of soluble manganese in the filtered water, free chlorine is added just prior to filtration to maintain a 0.3 to 0.5 ppm free residual in the filtered water.

The final residual disinfectant is accomplished by an application of chloramines to eliminate any post synthesis of THMs.

Although the individual cost of ozone generation is significant, it is offset by lower dosages needed for alum, chlorine and caustic soda. The anticipated chemical cost for the new Haworth Plant is 15% lower than the conventional costs.

The first section of the new ozone facilities was placed on-line on February 27, 1989 at a rate of 40 mgd. As the refurbishing of the original Haworth Plant reaches completion at the end of January 1990, the ozone facilities will be brought up to full capacity to handle the entire system demand.

OPERATIONS

During the three and one-half months of shakedown and subsequent full year of on-line operations, many interesting learning experiences occurred. The following is a recap of these experiences.

OZONE FACILITIES - AIR PREPARATION

The Haworth Plant utilizes air as the oxygen source. The system was designed for a constant air flow of 625 cfm. It was determined during the design phase that air-preparation equipment can be better specified for a constant flow. Therefore, there is one dedicated and independent air preparation system for each of the four (4) treatment trains.

A rotary lobe compressor collects filtered outside ambient air. The air then flows to dual compressor refrigerant dryers preceded by water pre-coolers. The dual compressors operate on a demand basis, depending on the air temperature and use ethylene glycol as the primary heat transfer agent. Following the refrigerant dryers are twin tower desiccant dryers using activated alumina as the absorbent. The towers are regenerated by external heat. The system brings the dewpoint of the air to -80°C; the specifications required -60°C.

Aside from typical bearing, relay and calibration problems, the most notable problem was the plugging of the float activated condensate drain line on one of the refrigerant dryers. This overloaded the refrigerant dryer which, in turn, overloaded the desiccant dryer and sent the dewpoint sky high. The ozone generators will trip out at a dewpoint of -50°C.

The fault was quickly found and remedied. Strainers were inserted just ahead of the float drains on each refrigerant dryer. These are periodically checked and cleaned.

OZONE FACILITIES - GENERATORS

The ozone generators are water-cooled, low frequency, horizontal glass dielectric tube units containing 900 individually fused dielectric tubes. Each unit can produce up to 700 ppd of ozone.

Aside from some vendor instrumentation and calibration problems, nothing unusual or of concern occurred with the ozone generators. However, it is interesting to note that, since the ozone production is controlled by off-gas concentration, the design concept was to apply ozone to just meet the ozone demand of the water and have very little ozone remain in the off-gas, perhaps as little as 300 - 400 ppm. Unfortunately, with the development of CT (cone. X time) values, achieving low off-gas levels results in no residual ozone and, thus, a CT of zero. At this point in time, we have raised the off-gas concentration set point from 400 to 1200 ppm of ozone in order to apply a higher dosage of ozone to the water in hopes of achieving some residual ozone.

It has become apparent that if CT is here to stay, then the proper technique for controlling ozone production is through residual analysis. Currently, we are looking at continuous analyzers for ozone in the aqueous phase utilizing membrane or air stripping methodology.

OZONE FACILITIES - TURBINE DIFFUSERS

Because of iron and manganese in our raw water and the potential for plugging of porous diffusers, we selected the mechanical turbine diffuser which is both self-aspirating and non-plugging.

The turbine diffusers are 100 horsepower, submersible units. Each turbine, by riding on a track to the underside of the top slab, are self-seating on their own pedestal when in place. Each of the four (4) ozone contactors contains one turbine unit. It was with these turbine units that the most difficult problems occurred during shakedown.

The turbine diffuser, in order to operate most effectively, has a narrow control range for gas flow and pressure. To control the gas aspiration rate, an orifice plate is generally used to set the water flow through the impeller eye and, thus, the aspiration rate. On paper this works very nicely, but the diurnal variation in air temperatures in New Jersey had serious effects on the ultimate volume of gas flowing to the turbine, thus affecting the flow and pressure, adversely affecting turbine performance. To correct this, a microprocessed turbine motor speed controller (frequency drive) was installed taking a signal from the ozone generator outlet pressure. This works superbly and there has been no recurrence of turbine diffuser performance problems since.

OZONE FACILITIES - CONTACTORS

The four (4) independent contactors are unique and were designed around the turbine diffuser. An 18-foot diameter column, 26 feet high, sits in the middle of a 55-foot square chamber, 30 feet high.

Coagulant treated water enters the 18-foot diameter ozone contacting column flowing downward toward the turbine diffuser and exits through bottom ports in the column into the outer square chamber where it flows upward to outlet weirs. The inlet to the contacting column is isolated from the outer square chamber and the area over the contacting column contains spray heads for foam suppression. The hydraulic residence time in the contacting column is nominally 2 minutes, and 18 minutes in the outer square chamber. Achieving the proposed CT valves within the contacting column may be a bit difficult, but if an ozone residual can be established in the outer chamber, then the higher residence time will be of benefit. We are working in this direction. Currently, with the higher applied ozone dosage, the transfer efficiency is around 90%. The full depth of water receiving ozone diffusing is 20 feet.

OZONE FACILITIES - DESTRUCT UNITS

The ozone destructors are of the thermo-catalytic type. Gas inlet temperatures are brought to 75°F. Manganese dioxide is the catalyst. A venting blower directs the off-gas to the destructor and is paced to maintain a slight negative head in the contactor head-space. After one year of operation, all vent blower seals were replaced. This may prove to be an annual activity.

FROTH REMOVAL - SKIMMERS

Because the ozone facilities are actually a retrofit to an existing conventional plant, all existing structures were retained. The original flocculation compartments were modified to accept skimming equipment.

The addition of coagulants at the ozone contactors results in the production of significant quantities of froth which is removed by the skimmers (chains and flights). It is estimated that 30-40% of the solids produced is removed by this process, thereby extending filter runs.

The most formidable and, as yet, unsolved problem with the skimming process is that the froth freezes quickly in the winter. We are looking for a low cost solution to this problem. Fortunately, the lack of froth removal during the colder months has not shown any deleterious effect upon finished water quality.

RETENTION BASINS

The original sedimentation basins have been retained and serve as flow-through conduits to convey the treated water to the filter buildings. It is estimated that perhaps 10% of the solids may be removed by settling.

FILTERS

Twelve (12) new filters were constructed, utilizing pre-cast concrete bottoms with high impact plastic nozzles. The original eight (8) filters of Wheeler pocket construction were modified to reflect the new flat bottom design. The use of nozzles allows the combination of air scour and water during the filter wash sequence.

The dual filter media were designed for maximum storage of floe within the anthracite layer, allowing the sand layer to act as a polishing medium. Each filter has a surface area of 1144 square feet. With a loading rate of 6 gpm/sq.ft., each filter can produce 10 mgd of water. Filter runs are averaging about 24 hours.

Our raw water contains manganese and it is known that ozone either will not completely oxidize manganese to the insoluble state or will oxidize it all the way to permanganate. It is also known that aged filter media, in the presence of an oxidant, will, through an auto-catalytic mechanism, remove soluble manganese. However, with new filter media, the active manganic oxide coating that provides the auto-catalytic reaction has not yet formed and manganese will pass these filters. At the Haworth Plant, we saved the old sand and placed six (6) inches of this aged material on each of the twenty (20) new filters to enhance the filter aging process. Prior to doing this, the manganese level in the filtered water was 0.08 ppm. After the addition of the aged sand, the manganese dropped to 0.03 ppm.

WATER OUALITY

Finished water quality was the prime consideration in the overall design of the Haworth Plant. During this first year of operation, the Oradell Plant was also in service. The Oradell Plant is a conventional treatment plant. A very interesting water quality comparison can be made, since both plants derive raw water from the same source. The following table looks at several finished water quality parameters.

Oradell Pilot Haworth

Plant Plant Plant

(Conventional Ozone (Ozone

Raw Treatment) Treatment Treatment)

Parameters (ppm) (ppm) (ppm) (Pam)

pH 7.6 8.0 8.0 8.0

Color 30 4 3 2

Turbidity 3.0 0.3 0.3 0.2

Taste & Odor earthy musty- slightly N.D.

chlorine sweet

Iron 0.19 0.02 0.03 0.01

Manganese 0.15 0.02 0.02 0.03

DBPs

THMs N.D. 0.074 0.019 0.021

Formaldehyde N.D. 0.008 --- 0.017

TREATMENT AND COST

The following table compares the various chemical dosages between conventional treatment and ozone treatment, as well as, that predicted by the pilot studies.

Oradell Pilot Haworth

Plant Plant Plant

(Conventional Ozone (Ozone

Treatment) Treatment Treatment)

(ppm) (ppm) (ppm)

Alum 18.0 8.0 7.0

Polymer 0.5 1.5 1.7

Ozone ---- 1.3 1.8

Pre-Chlorine 7.4 1.5 2.9

Post-Ammonia 1.3 0.4 1.0

Post-chlorine 1.6 1.0 2.1

Caustic soda 16.0 8.0 7.0

It is seen that direct filtration in this treatment process results in a significant reduction in alum, but a considerable increase in the use of polymer. The use of pre-ozonation reduces the overall need for chlorine and this, coupled with the lower alum dose, results in less caustic soda required.

The dosages predicted by the pilot studies are fairly accurate, with the exception of ozone and pre-filter chlorine. In the case of ozone, a higher dosage is being applied in order to achieve a measurable residual. A higher pre-chlorine dosage was necessary to maintain an active oxidation potential within the filter to effectively regenerate the auto-catalytic mechanism for removal of soluble manganese. The higher ammonia and post-chlorine dosages are commensurate with the carrying of a higher chloramine residual.

The following table compares the chemical treatment costs between conventional and ozone treatment.

Conventional Ozone

Treatment Treatment

(per mg) (per mg)

Alum $ 9.91 $ 3.85

Polymer 2.96 10.07

*Ozone ---- 10.21

Pre-chlorine 13.82 5.42

Ammonia 1.30 1.00

Post-chlorine 2.99 3.92

Caustic soda 20.95 9.17

TOTAL $51.93 $43.64

*Ozone: 10.4 KWH/lb Ozone = $0.68/lb

The overall reduction in the use of treatment chemicals has resulted in a 16% savings in chemical cost, compared to the conventional treatment process.

COMPUTER SYSTEM

The Plant also includes a computer system that, when fully installed, will enable the entire plant, including low and high lift pumps, chemical treatment, ozonation and filter operations, to be controlled from a central computer terminal in the Administration Building. Full assimilation and retrieval of historical plant data is part of the system.

OPERATOR TRAINING

During this same period, training of all plant operators was conducted using vendor, in-house and on-the-job training.

CONCLUSION

We are quite pleased with the first year of operation. Considering the complexity at the Haworth Plant, relatively few problems occurred. Water quality has followed pretty closely to that predicted by the pilot study with some parameters being surpassed and we have proved, that as far as operations are concerned, ozone is an economical and effective chemical.

By April of this year, the Oradell Plant will be taken off-line and the entire system demand will be derived from the Haworth Plant. The second year, with full plant flow, should prove even more interesting than the first year.