Abstract

Treatment of municipal liquid wastes generates immense quantities of sludges that demands environmentally safe disposal or reuse. The past 40 years have seen the emergence of an increasing desire worldwide to attenuate the disposal of biosolids to landfills and to promote the options of the agricultural application of this by-product as soil conditioner and fertilizer. Consequently, post-treatment steps are commonly required as a means to adapt biosolids to the requirements of environmental legislations. Conventional methods are not generally effective enough; hence, novel and emerging methods are continually being sought.
This study was initiated to develop an eco-efficient process that produces a pathogen-free biosolids product which can be used beneficially for land application
to meet or better stringent public health and environmental concerns. To achieve this goal BioElectroTM, an enhanced 2D electric field process, was developed. The biosolids treatment experiments were performed at the average initial temperature, pH and ORP of 18°C, 8.17 and -57.3 mV, respectively. Clostridium perfringens spores in anaerobically digested biosolids were used as the bioindicator to assess the eficiency of BioElectroTM process. It was evident that electrical field intensity
between 2.5-2.8 (V/cm) was capable of reducing the number of viable C. perfringens spores below ceiling levels (>3 LRs).
Furthermore, the mechanism of disinfection during BioElectroTM process was evaluated. Statistically significant effects of electric field intensity (E) and applied enhancement agents were ascertained at each time interval using multiple linear regression (MLR). Moreover, the shape of inactivation curves resulting from the
BioElectroTM treatment showed a triphasic pattern, starting with a short linear part at low treatment times, followed by a shoulder or a lag period and finally a first-order inactivation kinetics. This was explained by effects of multiple stressors and mechanism of disinfection during the BioElectroTM treatment. Ultrastructural analyses using transmission electron microscope were performed
to investigate physiological changes in the fitness of treated spores. It was observed that electric field can be considered as an inducing factor in activating and con-
sequent germination of dormant spore, and that can be responsible for shoulder formation in survival curves.
Also, an empirical model was developed by non-linear programming approach to quantify disinfection kinetics of BioElectroTM disinfection process. The proposed
model was able to predict the spore inactivation very accurately.