HAITH provide new Effluent Treatment System for E Park & Sons, Potato Merchants HAITH provide new Effluent Treatment System for E Park & Sons, Potato Merchants HAITH provide new Effluent Treatment System for E Park & Sons, Potato Merchants HAITH provide new Effluent Treatment System for E Park & Sons, Potato Merchants
 

HAITH provide new Effluent Treatment System for E Park & Sons, Potato Merchants

27th July 2006

Haith Industrial of Worksop, specialist in waste and water treatment have recently designed, manufactured and commissioned a new effluent treatment plant for E.Park and Sons of Doncaster.

E.Park and Sons are a family concern who has managed the business since 1924. The company specialise in marketing 130,000 tonnes of potatoes per year. Their Doncaster factory primarily supplies washed pre-packed potatoes to a number of major multiples.

Following several consultation processes Haith were tasked with designing a system to initially treat the current effluent stream from the pre-packing factory with an additional capacity to accept the future addition of potato processing effluent.

The design would enable a pre-treated effluent stream emanating from peeling and processing to be introduced into the system which would in turn be expanded to incorporate a secondary biological process called activated sludge.

Following treatment through all stages of the process including primary and carbon filtration Haith established that the effluent would be of a standard which would permit re-cycling to low care processes. This proportion of effluent re-cycled, being dependent on a number of parameters such as ambient temperature. Based upon their past experience Haith recommended that approximately 75% of the total effluent treated was re-used.

The process technology required to eradicate the intensive manual management of the water and silt was dealt with by the recommendation of the low manpower requirement and pressing capacity of a filter belt machine as being the most suitable. Filter belt machines have consistently proven to be able to tolerate the great variances in sludge loading which occur during periods when field conditions are bad and tubers are dirty.

Before making recommendations regarding the treatment philosophy for biological oxidation of the BOD, Haith took into consideration the highly variable organic nature of the effluent, particularly during the early season. Such variances can impact significantly on the biological process plant. These variances led to the selection of an attached growth system which is carried out in a SAF unit which provides the total biological treatment capacity for the pre-pack effluent, changing to a high rate roughing filter after the introduction of the processing effluent.

Such systems are simple to operate and have low operating costs, in addition is its ability to withstand shock and toxic loads owing to the relatively short contact time of the effluent with the slime layer. However, what are seen as the aerated treatment unit's greatest attractions are its low maintenance and management requirements.
Being high rate the main advantages of the aerated treatment unit are reduced power, maintenance costs, and stability against hydraulic shock loads.

Capable of achieving a high degree of carbonaceous and nitrogenous BOD removal; ponding of the bed, clogging of filter nozzles and odours and fly nuisance are also eliminated.

The new system provides solids / liquids separation of the pack house effluent prior to disposal. This filtration process removes a high percentage of the solids fraction contained in the effluent generating clear liquor. This has a beneficial effect of improving the standard of effluent discharged from site and deals with the solids on a continual basis in a manner that is automated.

As the solids removed are a combination of organic and inorganic inert material there is a reduction of Biochemical Oxygen demand, this reduction varying according to the quality of the produce washed, the set of the skins and other factors.

The removal of the solids fraction contained within the effluent is the first process to be undertaken before further processing such as microbial oxidation (BOD removal) is adopted. The effluent discharged from each of the washer lines flows via the existing floor gully system into an existing pump chamber. Haith modified this chamber by the addition of new course screening and mixing equipment. The existing pump was re-used to feed a new screen (paddle unit) with a higher capacity and capable of producing dryer screenings. This screen was located on top of the balance tank, and was fitted with a mechanical mixer to prevent settlement.

Level switches in the balance tank operate a submersible pump, which pumps the effluent to a clarifier. The level control operating this pump can also provide necessary control to stop and start the flocculent dosing pump. This addition of flocculent is required to achieve solids liquid separation within the clarifier giving rise to a thickened slurry underflow being discharged at its base and a clear supernatant being discharged over the weir plates at the top.

The sludge from the Clarifier is then pumped into a 12m-sludge balance tank fitted with a picket fence type mixer. This tank provides storage and mixing of the sludge prior to pressing and accepts any surges in sludge production that may occur.

From the balance tank the sludge is pumped at a controlled rate to the multi-roll belt filter to convert the sludge into a manageable cake of approximately 65%. The cake is then discharged onto an elevator conveyor that elevates the discharge to a height suitable for loading a standard farm trailer. The filtrate water from the sludge along with the belt wash water returns via a floor gully in the primary sump for re treatment.

Also associated with the plant is a flocculent preparation and dosing system that provides a usable flocculent solution to both the clarifier and press.

On completion of phase one the effluent is clarified but still has a residual BOD level, which will be reduced by bacteriological oxidation. This involves passing the clarified effluent through a Haith, single cell upward flow design SAF unit which is sized to reduce the BOD level to 10mg/l from approximately 250mg/l.

The bacteria supporting media selected for this specific form of treatment has high voidage to prevent blocking due to the high slime growth and subsequent sludge generation. In each cell the media is supported on galvanised steel ambi-deck panels mounted in a common frame. A holding down deck is secured to the top of the filter body to retain the "swelling" media during the establishing period.

Aerobic conditions are then provided in each cell by an aeration system comprising of E.D.P.M. Membrane diffusers mounted on a manifold, are then connected to a centrifugal type blower unit.

A base frame was supplied to distribute the weight of the filter over its base area and to also maintain the necessary height for gravity flow to a final settlement tank.

The conical bottom section of the tank included a cone and rake which encourages the sludge to compact and assists in its movement to the cone outlet.

At the upper edge of the parallel section a peripherally mounted external collection gallery collects the supernatant liquor. Fitted to the inner face of this launder is a set of v' notch weir plates fixed with stainless bolts which are adjustable to allow movement in the vertical mode. Haith also supplied a system to add nutrients to ensure the correct nitrogen and phosphate balance. Comprising of a 1000 litre storage dosing tank and positive displacement dosing pump, this combination offers the option of dosing liquid nutrient, ie: urea or powder such as ammonium nitrate.

Following biological treatment within the ATU the effluent is settled again to remove bacterial solids prior to filtration to remove the pesticide residues contained within the effluent stream.

This filtration process is conducted in two stages; sand filtration to polish the effluent and remove suspended solids in excess of 15 - 20 micron, followed by passing the filtered effluent through a secondary filter containing activated carbon. Thus the activated carbon acts as a catalyst which absorbs the soluble pesticides thus removing them from the effluent. The greater quantity of pesticides removed the more frequent the carbon has to be replaced and the old discarded, the anticipated life expectancy being 1 to 2 years.

Filtered effluent either discharges to the watercourse or passes to a storage tank from where the water can be re-used in the factory for filling washers. Haith recommended a maximum of 75% re-use of treated water to prevent increased background levels of nitrates etc.

Any treated water is then returned to the washers via the existing pipe work where a new pump and pressure bladder delivers the water through the underground pipe work which enters the factory.

To accommodate this, the isolation valve below the water storage tank was closed allowing only treated water to the washers through the fill pipe work. The pressure bladder being a pressure sensitive system detects a drop in line pressure, as would occur when the valve is opened to fill a washer. On detecting a pressure drop the pump starts and transfers the treated water. Closing the valve will build the pressure in the line and stop the pump.