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.本研究成功构建了微藻莱茵衣藻（Chlamydomonas reinhardtii）与坚强微杆菌（Microbacterium forte）的共培养菌群，用于修复高有机负荷的模拟乳制品废水（sDWW）及原乳制品废水（raw DWW），二者的化学需氧量（Chemical Oxygen Demand, COD）分别为12000 mg·L⁻¹与7346 mg·L⁻¹。该共培养体系在模拟乳制品废水中培养时，可获得大量生物质（最高可达11.27 g·L⁻¹，日产量达1.25 g·L⁻¹·d⁻¹），并产出生物氢气（14天后最高可达185.8 mL·L⁻¹）。此外，与单一细菌培养体系相比，共培养体系可降低71%~89%的二氧化碳排放。仅需添加微量元素即可使该共培养菌群在乳制品废水中生长，无需额外补充碳、氮、磷等其他主要营养物质。研究确定的最优生长条件为：光照强度120 μmol光子·m⁻²·s⁻¹，且无需搅拌。莱茵衣藻与坚强微杆菌之间形成了互利共生关系，可促进二者均实现大量生长。坚强微杆菌的蛋白水解活性及其后续释放的铵态氮，加之该细菌分泌的乙酸，构成了该互利共生关系的核心，推动莱茵衣藻实现高效的混合营养生长。本研究为工业规模下无法采用预处理工艺的高有机负荷乳制品废水的生物修复与资源化利用提供了潜在解决方案。