C214 - New Zealand Fish Products Ltd - Wellington Region

Summary
Fish odour and wastewater contamination have been significantly reduced through a number of CP options. In some cases investments were made to ensure compliance with environmental legislation. Total savings of over $100,000 have been made through reduced labour and trade waste costs.

Business Profile
New Zealand Fish in Petone is a fish-waste processing plant. Products include fish oil and powdered fish meal which are mainly exported to Asia.

Type of Project(s)
Process modifications and energy efficiency

Reasons for Project(s)
NZ Fish Products started looking into environmental issues in 1992 to comply with odour standards. In 1995, the company took part in a ECNZ waste minimisation project aimed to identify and implement cleaner production options to minimise waste. Since then the company has looked continuously into improving its environmental performance.

The Project

The liquor discharged from the decanter is pumped to a disc separator where free fish oil is separated from the aqueous phase and piped to bulk storage. The final wastewater stream, known as "stickwater", is disposed into the sanitary sewer as trade waste. The stickwater presently contains high levels of suspended and dissolved solids and a certain amount of oil and grease, in excess of normal trade waste acceptance standards.

Biofilter
A biofilter was installed to deal with fish odour released from the cooker, decanter and dryer. A biofilter is an extremely effective method of removing fishy odours from the plant ventilation air with the added advantage that it does not produce another waste stream in the process. The biofilter is a 1.8 metre deep bed of bark over a polyethylene pipe distribution network. The surface area of the bed is approximately 400 m2. Micro-organisms in the bark bed break the chemicals that cause the odour down. Minor problems occur when the plant starts up after extended down-time as the micro-organism population dies down when the biofilter is not used. This results in a short period of odour emission for 3-6 hours before the biofilter recovers. Air from the cooker and decanter is directly fed into the biofilter. The hot air from the dryer (80-90oC) is first passed through a wet scrubber and cooled to 30oC.

The installation of the biofilter cost approximately $70,000. No direct economic savings were made, but the biofilter has been effective in reducing odour since it was built in 1995. This brings the company into compliance with regional standards, and fewer complaints are received from neighbouring businesses.

Tanks
Until recently raw fish was delivered to, and stored in, the plant in 240L steel drums. As odour was a problem fish had to be processed the same night. As the council now requires fish to be transported in closed containers, five 8000L closed tanks have been installed inside the plant for fish storage. Fish is automatically and consistently drawn from tanks to the cooker, improving product quality. Labour time is saved due to reduced handling and cleaning time. Odour emissions from the tank are vented directly to the biofilter. Previously, fish had to be processed the same night because of odour nuisance. Now processing of fish has become more flexible as the fish can be stored in the closed tanks if the volume is not sufficient for processing. This flexibility allows the plant to fully operate at off-peak times when lower power rates apply.

Purchase and installation costs of the tanks were not provided, but Labour savings will be at least $20,000 per year. Other benefits include:

• Energy savings through off peak power use and water savings.
• Improved product quality
• Reduced water use and discharge from cleaning
• Reduced odour emissions
• Improved relationship with neighbouring businesses due to reduced odour nuisance

Efficient cooker
A more efficient cooker was purchased. Costs of the cooker were $15,000, and it provided energy savings of $3000 per year. The payback period is 5 years based on energy savings, however, increased efficiency and product recovery also provided significant savings. The benefits included reduced energy use and costs; improved product quality and increased product recovery; increased efficiency; and reduced emissions.

The dosing of sulphuric acid into the cooker must be accurate, as wide variations in pH are likely to adversely affect the product. Minor modifications were made to provide more consistent dosing. These included:

• installation of a holding tank to replace the current dosing bin

Purchase costs for the holding tank and for the global valve were approximately $4,000. There were no direct financial savings. The benefits were:

• consistent and optimised pH at the rendering stage.
• sulphuric pre-treatment of the protein before cooking.
• attenuation of flow changes into the rendering vessel.
• improved product quality due to more consistent dosing which has follow-on benefits for the rest of the plant.

Optimisation of decanter performance
Following the cooking process, the product solids are separated from the aqueous slurry using a decanter centrifuge. The performance of the decanter was optimised by the following:

• reduction of flow rate (speed at which fish slurry is fed into the decanter)
• increase of the weir height, which determines the depth of liquid maintained inside the decanter while it is rotating at speed
• increase of the scroll differential speed (speed at which internal screw rotates to separate solids from aqueous slurry)

Improved decanter performance resulted in improved product recovery and quality, and improved stickwater quality. The cost for staff and consultants was less than $2,000. Savings through increased product recovery and reduced trade waste charges are estimated at approximately $50,000 per year.

A trial is being undertaken to reduce the level of contamination in the stickwater by physiochemically treating it using flocculation, followed by dissolved air flotation (DAF). The method involves pre-treatment of the stickwater with flocculants to maximise the precipitation of proteins and reduce fish oil solubility. The precipitated products are then separated from the stickwater using dissolved air flotation. The obtained sludge requires further treatment for reuse. The quality of the effluent now meets regulatory requirements.

Capital costs are estimated at $155,000. Operating costs are approximately $4,000 per year. Expected savings are $20,000 per year due to a reduction in proposed trade waste charges. The sale of the thickened float as a fertiliser or the recovery of product from this may provide further economic savings.

For additional information contact:

Peter van Gosliga New Zealand Fish Products Ltd PO Box 33 166 Petone Phone: (04)-568 6966 Fax: (04)-568 9964

Opus International Consultants Ltd PO Box 12 003 Wellington Phone: (04)-471 7000 Fax: (04)-471 7770