藻菌共生系统处理畜禽沼液的机制及影响因素研究进展

Research progress on the mechanisms and influencing factors for the microalgae-bacteria symbiosis system for treating biogas slurry from livestock and poultry industry

畜禽沼液不仅含有高浓度氨氮、总磷、难降解有机物以及重金属和抗生素等风险因子,同时也存在大量有效氮、磷、钾等营养成分,未经过适当处理的沼液直接排放极容易造成水体的富营养化、土壤酸化和污染物累积等生态环境问题,加上沼液极具资源化潜力,因此对其进行有效的处理与资源再利用对于促进可持续发展具有重要意义。微藻细菌共生系统(藻菌共生系统)作为一种新兴的沼液处理方式,得到了广泛关注与研究。相较于传统的沼液处理方法,藻菌共生系统具有低成本、高效率、环境友好等优点,其不仅可高效去除沼液中的氮、磷、重金属、抗生素等物质,而且能同步利用CO_(2)进行光合作用,产生具有生物燃料潜质的微藻生物质,应用前景广阔。该文分析总结了藻菌共生系统的共生机制,概括了其类型,系统解析了其去除沼液污染物的机理,并重点阐述了藻菌共生系统的影响因素,最后讨论和展望了该系统所面临的挑战与未来的发展方向,以期为基于藻菌共生系统的沼液规模化处理及利用提供理论指导。

A large number of ancillary products are inevitably produced during the anaerobic digestion of livestock and poultry manure.Among them,biogas slurry contains a high number of available nutrients,like nitrogen,phosphorus and potassium,as well as amino acids,humic acids,and indoleacetic acids.Correspondingly,biogas slurry is often used in agricultural practices in the form of organic liquid fertilizer.However,there are also many pollutants in the biogas slurry,such as high concentrations of ammonia nitrogen,total phosphorus,heavy metals and some refractory organic substances including antibiotics.Therefore,the discharge of biogas slurry without appropriate treatment is extremely likely to cause ecological and environmental risks,such as water eutrophication,soil acidification,and pollutant accumulation.Nevertheless,the reclamation and reuse of biogas slurry can be expected as the potential of promoting a circular economy and sustainable development worldwide from the viewpoint of resource reutilization.Fortunately,the microalgae-bacteria symbiosis system can serve as an emerging technology to treat the biogas slurry in a sustainable manner in recent years.Much attention has been gained in the biogas slurry treatment,due to the lower cost,higher efficiency,and much more environmental friendliness than before.Particularly,the microalgae-bacteria symbiosis system can be used to efficiently remove nitrogen,phosphorus,heavy metals,and antibiotics,in order to provide the sound purification of biogas slurry.The contributions can also be found in the recovery of nutrients from biogas slurry and the utilization of CO_(2) for photosynthesis,leading to the microalgae biomass of biofuel value.Therefore,a systematic and latest review was proposed on this symbiosis system to consider the substantial development potential and great application prospects.The symbiotic mechanisms between microalgae and bacteria were first summarized,and then to provide a systematic review from the perspectives of the types of microalgae-bacteria symbiosis system,pollutant removal mechanisms and influencing factors.The symbiotic relationships between microalgae and bacteria included nutrient exchange,signal transduction,and gene transfer,thus supporting the operation of the microalgae-bacteria symbiosis system.Three types were divided,i.e.,free type,attached type,and microalgae-bacteria photobioreactor,according to the existential state of microalgae and bacteria in the system and development sequence.No matter what type the system was,it was necessary to fully coordinate the pre-treatment of biogas slurry with the docking of the reactor in the process of system establishment,in order to maximize the purification performance and resource utilization potential.Besides,an overview was provided on the system’s removal of nutrients(i.e.,nitrogen and phosphorus),refractory organic compounds,and heavy metals from biogas slurry.The microalgae-bacteria symbiosis system showed a lower energy demand and cost than before,indicating the effective performance of resource recovery.In addition,a brief discussion was conducted on the effects of microalgae-bacterial type/ratio and environmental factors(i.e.,nutrients,aeration rate,pH,temperature,light conditions,heavy metals,and antibiotics).The appropriate environmental factors and type/ratio of microalgae-bacteria played a crucial role in the better growth and metabolism of microalgae,the removal of pollutants,and the stability of the system.Finally,the main challenges of this system were proposed for the promising research directions.A relatively complex mechanism was found in the microalgae-bacteria symbiosis under the biogas slurry environment.By far,it was still unclear on the information about signal transduction and gene transfer between microalgae and bacteria.Besides,the promising directions were the coordination and docking between pretreatment and reactors.More importantly,the full chain of resource recycling can be realized from the notorious biogas slurry to the valuable microalgae biomass-based refined products.The study can also provide the scientific basis and theoretical guidance on the future large-scale application of microalgae-bacteria symbiosis system for biogas slurry treatment.