In many activated sludge wastewater treatment plants, a number of microorganisms are involved in the formation of foam.
Within these plants, a stable sludge layer may arise on the activated sludge tank as well as on the final clarifier. These problems find their origin in the growth of microorganisms such as filamentous bacteria, among which are the well-known “foam bacterium” or Microthrix parvicella. Similar sludge layers can also be observed in storage basins and within digesting devices.
Usually, a common technique for identifying bacteria which is carried out within many wastewater treatment plants is light microscopy. However, visual identification using such a technology is often difficult and unknown bacteria cannot be identified optically. In the same manner, most of these bacteria cannot be cultivated considering that the activated sludge is a complex ecosystem. As a result, cultivation is not a suitable identification technology either. To overcome these technical barriers, using the VIT kit system allows the operating staff to perform a fast and specific in situ bio sensing identification of bacteria. The gene probe, which constitutes the heart of the toolkit, is applied in the form of a solution to the dried activated sludge sample.
A good example of the VIT toolkit efficiency is illustrated by the targeted monitoring of the Microthrix parvicella that has been conducted at the wastewater treatment plant in Hetlingen (Germany). Initially, a number of lab-scale experiments were carried out. These trials aimed at reducing the sludge volume index (or SVI in mg/L) by using poly-aluminium hydroxy chloride (or PAC), which is a coagulant. The use of the PAC agent led to decrease the SVI from 270 ml/g to 150 ml/g. From then on, although a decrease was observed at the industrial scale, such an operation was not considered sustainable because of its non-cost-effectiveness; due to the high price of the PAC in comparison with traditional coagulants.
To improve the use of PAC, regular determination of Microthrix parvicella, using a VIT- Microthrix specific gene probe, has been carried out. Running such a control of the activated sludge has revealed the specific gene probe to be an effective early warning system for preventing an increase in the sludge volume. It has been shown there was a direct correlation between the amount of this organism and the sludge volume index so that the increase of the sludge volume index was following the increase of Microthrix parvicella. In addition, as the growth of Microthrix parvicella was initiated within the sludge, it was not possible to observe it with light microscopy, whereas the gene probe was perfectly suitable for both analysing and quantifying filaments of Microthrix parvicella.
As a result, thanks to the targeted monitoring of Microthrix parvicella with the VIT- Microthrix specific gene probe, coagulation with PAC is used sporadically as a temporary solution rather than as a routinely protocol. As well as being an analytical efficient solution, gene probe monitoring has shown to be a cost-saving operation.