Valorization of dairy wastewaters: large biomass and hydrogen production using an alga-bacterium consortium

The microalgae Chlamydomonas reinhardtii and the bacterium Microbacterium forte have been successfully cultivated as a consortium for the bioremediation of simulated dairy wastewater (sDWW) and raw DWW with high organic loads (Chemical Oxygen Demand (COD) of 12,000 and 7,346 mg·L-1, respectively). The coculture allowed the obtaining of large amounts of biomass (up to 11.27 g·L-1/ 1.25 g·L-1·d-1) and the production of biohydrogen (up to 185.8 mL·L-1 after 14 days) when cultivated in sDWW. Moreover, the use of cocultures reduced CO2 emissions (71-89%) compared to sole bacterial cultures. Supplementation with trace elements was sufficient to allow the consortium to grow in DWW without requiring other major nutrients such as carbon, nitrogen or phosphorus. Illumination at 120 µmol photon·m-2·s-1 and no agitation were identified as optimal growth conditions. Chlamydomonas and M. forte established a mutualistic relationship that facilitated substantial growth of both the bacteria and the alga. The proteolytic activity of M. forte and the subsequent release of ammonium, along with the excretion of acetic acid by the bacterium, represent the core of the mutualistic relationship that enabled significant mixotrophic growth of Chlamydomonas. This study presents potential solutions for the bioremediation and valorization of DWW with high organic loads, where the use of pre-treatment methods is not feasible on an industrial scale.

微藻类生物衣藻（Chlamydomonas reinhardtii）与细菌类微生物杆菌（Microbacterium forte）已成功作为共生体系在模拟乳制品废水和未经处理的乳制品废水中进行生物修复，其中乳制品废水具有高有机负荷（化学需氧量（COD）分别为12,000 mg·L-1和7,346 mg·L-1）。该共生体系在模拟乳制品废水中培育时，可产出大量生物质（高达11.27 g·L-1/ 1.25 g·L-1·d-1）并产生生物氢（14天后可达185.8 mL·L-1）。此外，与单一细菌培养相比，使用共生体系可显著降低二氧化碳排放（降低幅度为71-89%）。通过添加微量元素，即可使共生体系在未经处理的乳制品废水中生长，而无需添加其他主要营养物质，如碳、氮或磷。光照强度为120 µmol photon·m-2·s-1且无需搅拌已被确认为最佳生长条件。衣藻与M. forte建立了互利共生关系，促进了细菌与藻类的显著生长。M. forte的蛋白酶活性及其随后释放的铵以及细菌排泄的乙酸构成了互利共生关系的核心，这促进了衣藻的显著混合营养生长。本研究提出了针对高有机负荷乳制品废水的生物修复和增值的潜在解决方案，在这些情况下，工业规模上的预处理方法不可行。