Cycle 6 (2017 Deadline)
Evaluation of algal treatment options for olive mill wastewater to produce energy and biofertilizer
PI: Sami Sayadi, firstname.lastname@example.org, Center of Biotechnology of Sfax, Tunisia
U.S. Partner: David Blersch, Auburn University, and Walter Mulbry, (Ret.) USDA/ARS
Project dates: December 2017 - November 2020
The conventional olive mill wastewater (OMW) treatment methods adopted in Tunisia are either costly or ineffective,causing environmental pollution. This project is aimed at developing an eco-friendly and cost-effective microalgal-based process for olive mill waste treatment and recycling. Such a process should result in the production of (1) treated and reusable OMW for ferti-irrigation use, contributing to resolving the water scarcity problem; (2) renewable biomass useful for clean energy production, particularly bio gas; and (3) bio-fertilizers for agricultural use, using the process by-products, bio char and sludge.
|Indoor micro-algae cultivation in pre-treated Olive Mill Wastewater samples [Photo courtesy of Prof. Sayadi] |
The goal of this project is to develop an eco-friendly technology for creating a closed loop process with zero waste. It encompasses several disciplines and couples physical and biological technologies to achieve the target objectives, including pyrolysis, physical adsorption, micro algae cultivation with OMW treatment and CO2 mitigation, anaerobic digestion, and composting. The project will also foster linkages among the R&D sector (universities and research institutes) with enterprises involved in waste production (farms and olive mills), enterprises producing devices necessary for treatments, enterprises interested in the use of by-products, and farmers. This approach will create a cooperative network for reducing agricultural waste impacts on the environment, exchanging know-how and market intelligence, and developing research capacity and new markets. In particular, the enterprises will be involved in the demonstration activities of proposed technologies. Through the project, valuable resources that are not currently utilized will be exploited and thus will generate local added value in Tunisia. Such an integrated eco-technology should facilitate the production of biogas from the produced micro-algal biomass for electrical and heat energy generation, as well as biodiesel production, the extraction of high-added-value molecules for cosmetics and nutraceutical applications, nutrient recovery in the form of sludge and biochar for soil amendments, and treated OMW for ferti-irrigation use. This eco-technology will also improve the quality of life for local residents living near the OMW discharge area by reducing the environmental footprint of the existing evaporation ponds, in particular reducing populations of mosquitoes and noxious odors from the ponds.
Beyond the technological aspects, the project will also involve the collection and assessment of data to support decision-makers for the promotion of sound strategies and best practices for social, economic, and legislative measures at the regional and national levels regarding agricultural waste management. It is expected to generate business opportunities and create jobs in small and innovative companies for commercializing the process outcomes. The research team will also strive to enhance the impacts of the project by organizing roundtables and training workshops for farmers to help them better exploit the anticipated research results with regard to ferti-irrigation and soil fertilization.
During April-June 2018, the research group at the CBS continued their research work and conducted work on: (1) OMW pretreatment by biochar and (2) Microalgae cultivation using the pretreated OMW.
For the pretreatment tests, the PhD student continued her work on the discoloring of the OMW using biochar and commercial activated carbon (CAC). The investigations covered batch experimental tests as well as continuous flow column under laboratory conditions.The main effects of the process variables such as polyphenols concentration, adsorbent dosage, OMW pH and the interactions between these variables during the adsorption process were studied and evaluated using an experimental design. The removal of the polyphenols, COD and color from OMW were considered as process responses to be evaluated and optimized. The obtained results showed that a second-order model is appropriate to predict the discoloring of OMW. In addition, the adsorption of polyphenols from OMW on CAC was analyzed with the Langmuir, Freundlich and Temkin isotherms. The straight lines generated from the experimental data with a good correlation coefficient (R2=0.994) showed the acceptability of the Langmuir isotherm over other adsorption isotherms.
Two Post Doc candidates undertook substantial research work in cultivation of Microalgae using the pretreated OMW. Firstly, the microalgae strain Scenedesmus sp. was selected for the cultivation tests at the lab scale using OMW pretreated in different conditions. In order to evaluate the capacity of this strain in the removal of the major pollutants from OMW, a set of experiments using four types of pretreated OMW as culture medium, namely OMW treated by ultrafiltration (UF), OMW treated by electrocoagulation (EC) and OMW treated by adsorption on activated carbon using two different conditions (AC1 and AC2), was conducted. Each medium was used at different concentrations of 10, 25, 50 and 100%. Prior to the cultivation experiments, the team performed characterization of the culture media (UF, EC, AC1 and AC2). Results demonstrated that the strain was able to adapt to the high concentration in the medium of EC, AC1 and AC2 while it was stressed when using 100% of UF. A decrease in TOC concentration between 54% and 94% was determined using the six culture media. Concerning polyphenols removal, this varied from 47% to 73% when using the medium UF, the maximum was determined at UF10%. It varied from 40% to 100% with EC samples. The medium EC 50% and AC1 100% were selected for the next experiment. The strain was cultivated in a bubble column reactor using the selected media. Pollutants were eliminated at percentages of 66.80% and 46% for TOC and 61.50% and 100 % for polyphenols, using EC50% and AC1 100%, respectively. The produced biomass from the medium EC50% showed high proteins content of 46.90% whereas 56.80% of carbohydrates were determined when using ACA 100%. Secondly, the effects of raw OMW, UF and tyrosol (T) on growth, biochemical and physiological composition of Scenedesmus sp. have been investigated during single and two stages cultivation tests. During two stage cultivation, the addition of 80% OMW for 4 days was performed and the lipid and polyphenols content were evaluated. During single stage cultivation, lipid, protein and carbohydrate content were evaluated using the different culture media. Higher biomass yield was found compared to two stages. These results show that single stage cultivation can be considered as an efficient strategy to enhance biofuel production potential of Scenedesmus sp. In addition, these tests revealed that high antioxidant activity was obtained (characterized using three tests: DPPH, reducing power and ABTS). Indeed, the phenolic extracts of Scenedesmus sp. have an important antioxidant capacity. Scenedesmus sp. exhibited high polyphenol removal efficiency. BPA removal was mostly attributed to biodegradation. These results were confirmed by HPLC analysis of polyphenols. Oxidative stress was induced in Scenedesmus strains when exposed to increasing T, OMUF and OMW concentrations, as evidenced by increased malondialdehyde content. T, OMUF and OMW exposure also resulted in an over-expression of catalase antioxidant activity in Scenedesmus sp.
The project members held regular meetings to discuss the ongoing research work, the obtained results, and the forthcoming activities.
Project Website: The team launched the project website www.omw2algae.com featuring an overview of the project concept, objectives, and activities along with other details, which will be updated as the project progresses.
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|Team member with the student sampling Olive Mill Wastewater from storage and evaporation ponds||Truck tankers discharging Olive Mill Wastewater in storage and evaporation ponds |
In the upcoming three months, the research group will continue the work on OMW pretreatment and microalgae cultivation to identify the most promising process pathways. For the OMW pre-treatment task, additional experimental tests will be conducted on the continuous flow column using activated carbon and biochar in order to prepare the up-scaling of the pretreatment process and to produce additional quantities of pre-treated OMW which will serve for the microalgae cultivation tests in bench scale reactors. Microalgae cultivation research in different pre-treated media will be ongoing with the consideration of the limiting parameters of the process such as the dilution of the culture media. The microalgae growth and productivity will be evaluated and the influence of culture media and process parameters will be correlated with the composition of the produced biomass. The removal extent of the residual pollutants by the microalgae strain will also be monitored. The team will also start working on Biogas production from the produced microalgae biomass”. As preliminary work, the characterization of microalgae biomass will be carried out in order to determine the biochemical composition and the fatty acid profile and content. The optimization of cell lysis (cell disruption) of microalgae cells will also be conducted. The potential valorisation pathways will be investigated including high value molecules recovery and lipid extraction for biodiesel production.
The planning and preparation to visit the US partner will also be considered in the upcoming period.
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