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Are you pouring money down the drain?

30 September 2019

Keith Hutchings questions how much thought the food and beverage industry is giving to reducing the water used in the food production process. 

Process wastewater sent to a sewer attracts a ‘Trade Effluent Charge’ which will vary depending on effluent volume and quality. If the cleanliness of effluent can be improved then discharge costs can be reduced.

Wastewater disposal charges are based on the volume discharged and how much treatment it will need. Utility companies use the Mogden Formula to work this out. There are four parts to the formula and at each stage the costs can be decreased by treating or recycling water on site. 

Reception: the volume of wastewater discharged.

Level of treatment at the works: this could be a discharge straight to the sea or may need to run the wastewater through primary, secondary or tertiary treatment process.

Chemical Oxygen Demand (COD) of the wastewater: this charge is based on the ratio of what is discharged over the average discharge of a municipal customer of the local water company.

Solids content: this charge is also based on the ratio of what is discharged over the average municipal customer of that water company.

Reducing effluent
One way to reduce trade effluent charges is to reduce the amount of treatment required by removing the solids load. This process will vary depending on the amount and type of solids. 

Fruit and vegetable processing operations can incur high sewer discharge charges due to the amount of solids and Biological Oxygen Demand (BOD) present in the effluent water. The washing down of plant equipment and clean-in-place (CIP) activities can also dislodge processed product along with inorganics, such as sand and dirt, that will be washed away with the cleaning water. 

Sand and dirt can also damage processing equipment, causing equipment to prematurely fail or require reduced maintenance intervals, resulting in increased downtime.  

Fruit and vegetable processing wastewater may also have significant levels of TSS – the portion of fine particulate matter larger than two microns that remains in suspension in water. 

Flume receiving stations also require lots of water, and plants with conventional technologies are often left with no option other than to send flume water to large settling basins that require dredging, excavating, and hauling to regain volume for settling. One way to remove these solids is to feed the wastewater into settling ponds or lagoons and allow the solids to slowly settle to the bottom. These lagoons often have a large overall footprint and will require periodic dredging to remove the solids build-up and restore capacity. 

Other options include small-footprint hydrodynamic separation systems, such as the Grit King or TeaCup, which remove grit, sand and other inorganic solids, protecting downstream systems from clogging and abrasive damage, and negating the need for large settling tanks.

Liquid/solids separation systems can be optimised to remove abrasive particles from flows to cost-effectively protect plant. Technologies are available which can capture more, and finer, sand particles and, in most applications can remove more than 95% of grit 75 micron (200 mesh) and larger and these separation systems are retrofittable into existing process systems.

In many food processing applications once the dirt and debris has been removed by a separation system the water can be recycled for immediate re-use upstream to wash or convey additional product or reused in other plant operations.  

Typically, a screening and dewatering system is required before effluent is passed to a Dissolved Air Flotation (DAF) plant to remove fine particles, oils and grease.  

A rotating belt filter system can also provide screening and dewatering for food processing applications. One such system, which can replace conventional screen and dewatering systems in one step is the Hydro MicroScreen.  

Hydro International has created a free online calculator – hydro-int.com/trade-effluent – which shows how much its treatment systems can save on trade effluent costs.

Keith Hutchings is Europe product manager – Industrial & Municipal at Hydro International.


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