The foul smells from the Sant’Antnin recycling plant in Marsascala may be generated by certain processes, according to Wasteserv.
The waste agency yesterday said it was carrying out tests to find the cause.
It said the new management had inherited a lack of preventive maintenance programmes and serious design flaws in the plant.
The flaws led to serious damage in one of the tanks that stored material from which biogas was produced.
Wasteserv was reacting to questions raised by Nationalist MP Charlo Bonnici.