Enhanced Bioremediation Of Petroleum-contaminated Coastal Soil By Marinealgal Hydrolysate

Petroleum is an important energy and industrial raw material in the modern society.With the rapid development of economy,the application of petroleum and its products is more and more extensive.The exploitation of offshore oil resources and the sea transportation of petroleum have caused serious pollution in various coastal areas.Meanwhile,the coastal soil is often suffering from salinized due to the effects of seawater intrusion.Bioremediation is one of the most effective and widely used method to eliminate the contamination of petroleum in diverse environments.However,there are many factors limiting the application of bioremediation in the coastal soils that are impaired by salinization and petroleum contamination.The low level and imbalance of nutrients can significantly inhibit the reproduction and metabolism of microorganisms,resulting in the reduction of petroleum bioremediation efficiency in the salinized coastal soils.Therefore,it is necessary to add some nutrients to the salinized coastal soils for the improvement of petroleum degradation by microorganisms.Unfortunately,the most widely used method of adding inorganic nutrient to promote the petroleum degradation still has many problems,such as high cost,poor sustainability and secondary contamination.In the industry of fine chemicals production with seaweed as raw material and seaweed aquaculture,a large number of seaweed wastes are produced,which are riched in fiber,protein,carbohydrates and other organic substances.Most of these wastes have not been fully utilized,leading to the pressures on the receiving environments.Based on these information,the present study proposed to use seaweed wastes as experimental material to prepare marinealgal hydrolysate,and use marinealgal hydrolysate to produce the high efficiency petroleum-degrading bacteria agent for bioremediation of petroleum in salinized coastal soil,which provided a new idea for the enhancing bioremediation of the petroleum contaminated coastal soil and the utilization of seaweed wastes simultaneously.To our best knowledge,there are no reports about the use of marinealgal hydrolysate to enhance bioremediation of petroleum contaminated environments.Firstly,the seaweed waste was treated by hydrothermal lysis process,and the process parameters were optimized.The optimum technological conditions for the hydrothermal lysis of the seaweed waste were as follows: the hydrothermal temperature was 160 ?,the hydrothermal time was 120 min,and the ratio of seaweed waste and water(m/v)was 1:40,the marinealgal hydrolysate contained had emulsification and surface activity as well as multiplenutrients such as total sugar,reducing sugar,protein,acetic acid,nitrogen,phosphorus inorganic salts.The flask experiment of petroleum degradation showed that bacteria from coastal soil have the ability to petroleum degradation.The efficiency of petroleum degradation by coastal soil bacteria could be promoted when marinealgal hydrolysate as the growth substrate.Subsequently,the petroleum-degrading bacteria agent was prepared by culturing coastal soil bacteria based on marinealgal hydrolysate,and the experiment of petroleum degradation by this agent was conducted.When the concentration of the bacteria was OD600=1.6 in the agent,the petroleum degradation rate was 62.4% after 7 d for the10000 mg/L petroleum.Secondly,the effects of different strengthening methods,different adding proportions(v/m)and different petroleum pollution levels on the bioremediation effects of coastal petroleum contaminated soil were investigated.The results showed that the bioremediation of petroleum contaminated soil could be enhanced by marinealgal hydrolysate and petroleum-degrading bacteria agent.The best bioremediation effect was achieved when both of them were used together.When the proportion of marinealgal hydrolysate and petroleum-degrading bacteria agent was not more than 10%,the increase of proportion could significantly promote the degradation of petroleum.In contrast,when the proportion was more than 10%,the petroleum degradation rate changed little.The best bioremediation efficiency(the petroleum degradation rate was above 67%,up to 70%)could be obtained in the petroleum concentration ranged from 1000 to 5000 mg/kg.When the pollution level was more than 5000 mg/kg,the petroleum degradation rate began to decline.At last,the marinealgal hydrolysate and petroleum-degrading bacteria agent were used as bioaugmentation agents and added separately to the coastal petroleum contaminated soil with petroleum concentration of 1970 mg/kg in 10% adding proportion.After bioremediation of 40 d,the petroleum concentration decreased from 1970 mg/kg to 498 mg/kg(the petroleum degradation rate was 74.7%).The soil petroleum concentration had basically reached the two level environmental standard for the petroleum hydrocarbon concentration of the national agricultural land.The promoting of petroleum degradation in coastal soil could be due to the increase of soil dehydrogenase activity by marinealgal hydrolysate and petroleum-degrading bacteria agent.Marinealgal hydrolysate and petroleum-degrading bacteria agent could also increase the contents of soil organic matter,ammonium nitrogen,available phosphorus and rapidly available potassium,as well as improve the soil fertility to a certain extent.