Wastewater treatment from a science faculty during the COVID-19 pandemic by using ammonium-oxidising and heterotrophic bacteria

During and after the pandemic caused by the SARS-CoV-2 virus, the use of personal care products and disinfectants increased in universities worldwide. Among these, quaternary ammonium-based products stand out; these compounds and their intermediates caused substantial changes in the chemical composition of the wastewater produced by these institutions. For this reason, improvements and environmentally sustainable biological alternatives were introduced in the existing treatment systems so that these institutions could continue their research and teaching activities. For this reason, the objective of this study was to develop an improved culture medium to cultivate ammonium oxidising bacteria (AOB) to increase the biomass and use them in the treatment of wastewater produced in a faculty of sciences in Bogotá, D.C., Colombia. A Plackett Burman Experimental Design (PBED) and growth curves served for oligotrophic culture medium, and production conditions improved for the AOB. Finally, these bacteria were used with total heterotrophic bacteria (THB) for wastewater treatment in a pilot plant. Modification of base ammonium broth and culture conditions (6607 mg L⁻¹ of (NH₄)₂SO₄, 84 mg L⁻¹ CaCO₃, 40 mg L⁻¹ MgSO₄·7H₂O, 40 mg L⁻¹ CaCl₂·2H₂O and 200 mg L⁻¹ KH₂PO₄, 10% (w/v) inoculum, no copper addition, pH 7.0 ± 0.2, 200 r.p.m., 30 days) favoured the growth of Nitrosomonas europea, Nitrosococcus oceani, and Nitrosospira multiformis with values of 8.23 ± 1.9, 7.56 ± 0.7 and 4.2 ± 0.4 Log₁₀ CFU mL⁻¹, respectively. NO₂⁻ production was 0.396 ± 0.0264, 0.247 ± 0.013 and 0.185 ± 0.003 mg L⁻¹ for Nitrosomonas europea, Nitrosococcus oceani and Nitrosospira multiformis. After the 5-day wastewater treatment (WW) by co-inoculating the three studied bacteria in the wastewater (with their self-microorganisms), the concentrations of AOB and THB were 5.92 and 9.3 Log₁₀ CFU mL⁻¹, respectively. These values were related to the oxidative decrease of Chemical Oxygen Demand (COD), (39.5 mg L⁻¹), Ammonium ion (NH₄⁺), (6.5 mg L⁻¹) Nitrite (NO₂⁻), (2.0 mg L⁻¹) and Nitrate (NO₃⁻), (1.5 mg L⁻¹), respectively in the five days of treatment. It was concluded, with the improvement of a culture medium and production conditions for three AOB through biotechnological strategies at the laboratory scale, being a promising alternative to bio-augment of the biomass of the studied bacteria under controlled conditions that allow the aerobic removal of COD and nitrogen cycle intermediates present in the studied wastewater.