This paper presents the potentials of using biogas production and hydrogen sulphide concentration as the
parameters to regulate the oxygen supply to microaerobic reactors in order to control the biogas sulphide
content. Research was carried out in two identical bioreactors of 200 L at 35C and 19 d of hydraulic
retention time. The feed consisted of mixed sludge from a municipal wastewater treatment plant with
variable organic and sulphur load. The oxygen flow rate was automatically adjusted according to the biogas sulphide content (which ranged from 0.62 to 0.24%v/v) by a feedback Proportional-Integral-Derivative controller. The target hydrogen sulphide concentration (0.01%v/v) was achieved in 4.0–5.5 h. The
micro-oxygenation level reached was considered to be the optimum in the short-medium term, since
it kept the removal efficiency above 99% and minimised the oxygen concentration in the biogas during
the days following the controller application. Specifically, the average biogas oxygen content was
0.09%v/v. Subsequently, biogas production was used as the parameter to regulate the oxygen supply.
When the biogas sulphide content was around 0.33 and 0.50%v/v, approximately 3.5 and 5.0 NL of oxygen
were supplied per N m
3
of biogas (respectively). An average sulphide removal efficiency of 99%, and oxygen concentrations in the biogas of less than 0.08%v/v were achieved. Biogas production could be
employed to develop precise control strategies during microaerobic digestion under variable organic load
and steady sulphur load. Under unstable sulphur load, biogas sulphide content should be used instead.