Christopher Garton (Watercare Services Ltd)
An innovative chain dragging method invented by this author has been proven to be extremely successful at controlling nuisance Chironomus zealandicus midges at the Māngere Wastewater Treatment Plant (WWTP). This method replaced the
use of a chemical called methoprene which was used as a larvicide. Since the new method was used there have been fewer midges and more importantly fewer public complaints. The new method has also led to a 75% reduction in the operational budget from approximately $300,000 per annum to approximately $75,000 per annum.
C. zealandicus midges have plagued the neighbouring community of Māngere Bridge since the Māngere WWTP was first built in 1960. Methoprene was used very effectively to control the adult midge population from 2008 onwards but the Māngere WWTP still received midge-related complaints from the public. In 2017, methoprene was successfully replaced as the primary form of midge control with the innovative chain dragging method. Between 2017 and 2019 there were multiple experiments and modifications to the method to refine its effectiveness. Since October 2019 there have been no complaints from the public and the number of midges each season has been the lowest since records began. Therefore, there is now strong evidence that this new chain dragging method is a success. In 2019 this method also successfully replaced methoprene on Pond 1 at the Rosedale WWTP in Auckland.
This paper discusses the success of the method over the seasons. It also details how the method works including the frequency of application so that others in the water industry may adapt this method for their sites. This paper also discusses lessons learnt by the author. This midge control method has been a successful innovation from Watercare Services Limited and is an idea worth sharing with the wider water industry.