Wastewater treatment plants produce solid and semi-solid sludge, which treatment minimises secondary environmental pollution because of wastewater treatment and obtaining new bioproducts. For this ...reason, in this paper, the co-pyrolysis of biogenic biomasses recovered from a biological reactor with immobilised fungal and bacterial biomass and a tertiary reactor with
Chlorella
sp. used for dye-contaminated wastewater treatment was carried out. Biogenic biomasses mixed with pine bark allowed the production and characterisation of two types of biochar. The raw material and biochar were on the “in vitro” germination of
Lolium
sp. seeds, followed by adsorption studies for malachite green (MG) dye using the raw material and the biochar. Results showed that using 60 mg L
−1
of a cationic coagulant at pH 6.5 allowed for the recovery of more than 90% of the microalgae after 50 min of processing. Two biochar resulted: BC
300
, at pH 5.08 ± 0.08 and BC
500
, at pH 6.78 ± 0.01. The raw material and both biochars were co-inoculated with growth-promoting bacteria; their viabilities ranged from 1.7 × 10
6
± 1.0 × 10
1
to 7.5 × 10
8
± 6.0 × 10
2
CFU g
−1
for total heterotrophic, nitrogen-fixing and phosphate-solubilising bacteria. Re-use tests on
Lolium
sp. seed germination showed that with the post-coagulation effluent, the germination was 100%, while with the biochar, with and without beneficial bacteria, the germination was 98 and 99%, respectively. Finally, BC
500
adsorbed the highest percentage of malachite green at pH 4.0, obtaining
q
ecal values of 0.5249 mg g
−1
(
R
2
: 0.9875) with the pseudo-second-order model.
