Overview

McConnell Dowell Contractors found their current Pumice media provided poor drainage which was crucial in the wastewater filtration process. This means that with their current solution, the Biofilter fills with water and then creates short cutting patches, which doesn't allow the bacteria in the biofilter to remove the odours (VOC gases).

Background

McConnell Dowell Constructors manage the Mangere WWTP for Watercare. This site currently processes 50-60% of Auckland City’s waste, through a series of different processes, which removes waste solids, treats and neutralises the water and then discharges it safely back into the Auckland Harbour. 

The purpose of a biofilter is to remove VOC (Volatile Organic Compounds) that are released as gases, during the wastewater filtration treatment process. As the waste flows through the series of processes, high levels of VOC gases are captured and filtered through the biofiltration bark media, which works to remove and neutralise unpleasant odours.

Challenges

The pumice media currently used has poor drainage, which is essential for effective wastewater filtration. This results in the biofilter becoming waterlogged, leading to the formation of shortcutting patches where water bypasses the filtration process.

Consequently, the bacteria in the biofilter are unable to efficiently remove the odorous volatile organic compound (VOC) gases

Assessment

Due to the ongoing challenges that they were experiencing with their Pumice Biofiltration, McConnell Dowell Constructors felt they needed to explore other alternatives. Azwood were contacted following a recommendation from their consultant regarding a new recipe to try and mitigate their issues. 

The original recommended recipe had too many variables and was not a proven solution, therefore we offered an alternative solution which is our Biofilm Max c/w Ocean Shell, a tested and trusted solution used by many other wastewater filtration businesses around NZ.

Outcome

Azwood’s natural biofilter media is generated from two naturally derived products, Pine Bark Nuggets (derived as a forestry residue), and Ocean Shell (derived from the mussel fishing industry).

Our recommended recipe has different sizes of chipped/mulched timber at varying stages of the aging process as well as composted bark fines and ocean shell. This blend would allow for sufficient drainage while maintaining an optimum pH level.

The premium Biofilm bark nuggets encourage the bacteria within the natural biofilter media to thrive, which assists in the removal of the VOC odorous gases. The challenge any biofilter faces is the ability to maintain a level PH for optimum performance, this is where the ocean shell as a natural source of calcium helps to assist with maintaining the level PH.