## 3 Results and Discussions  
### Impact of Liquid-Digestate Dilution on Microalgae Growth on Batch Conditions  
Microalgae growth was tested by using three different digestate dilution (1:20; 1:30; 1:50) as culture media. The optimum dilution factor of the digestate was studied in batch mode in indoor condition in order to determine its feasibility as nutrient supplier for microalgae growth. Growth characteristics of _Monoraphidium_ sp. cultivated in digestate diluted 1:20, 1:30 and 1:50 where investigated within 25 days as shown in Figure 2. As a result, specific growth of 0.03, 0.05 and 0.13 d\({}^{-1}\) were calculated for digestate dilutions of L 20, L 30 and L 50 respectively (Figure 2a). In the case of low diluted digestate (L 20), the microalgae growth noticeable decelerated after 12 days, due to probably the high turbidity and the high initial ammonium concentration (98.8 mg L\({}^{-1}\)), which can presents toxicity for microalgae cells [11; 19]. [PERSON] et al. (2014) reported similar specific growth rate ranging from 0.05 and 0.09 d\({}^{-1}\) when the microalgae _Monoraphidium_ sp. T4X was cultivated under six different nitrate concentration [34]. Our results and dilution rate applied are quite lower to previous studies that investigated microalgae growth on diluted digestate but using different microalgae species [12; 13; 35]. [PERSON] et al. (2013) have investigated the cultivation of three microalgae strains (_Neochloris oleabundans, Chlorella vulgaris and Scenedesmus obliquus_) on an agro-zootechnical digestate at different dilution ratios (1:10; 1:15; 1:20: 1:25) [12]. At a dilution rate of 1:20, specific growth rate of 0.26, 0.23, 0.49 d\({}^{-1}\) were respectively observed for _Neochloris oleabundans, Scenedesmus obliquus and Chlorella vulgaris_[12]. [PERSON] et al. (2014) reported value of growth rate for _Scenedesmus sp._ ranging from 0.04 to 0.9 d\({}^{-1}\) at different inoculum/substrate ratio [35]. The dilution ratio that should be applied to improve microalgae growth by minimizing ammonia and turbidity toxicity is highly dependent on the liquid digestate nature and origin but value from literature are ranging from 1:10 until 1:100 [12; 19; 36]. To improve the overall environmental and economic feasibility of the process, it can be planned as future works to replace part of the tap water by agro-industrial wastewaters to reduce the ALD turbidity.  
The batch with higher dilution has better response to nutrients assimilation; therefore, microalgae growth is more feasible. After 25 days, 34, 66 and 100% of NH\({}_{4}^{+}\) were removed from media, from less to more diluted digestate respectively (Table 2). Similarly, P removal of 0, 77 and 92% were observed from less to more diluted digestate respectively. Nutrient removal efficiency for N and P is in agreement with previous studies that investigated microalgae growth on diluted digestate [12; 19]. At day 19, the culture with the lowest dilution collapsed and was not able to assimilate more nutrients (Figure 2c,d).  
Figure 2: (**a**) Growth curves and (**b**) NH\({}_{4}\)\({}^{+}\), (**c**) NO\({}_{3}\)\({}^{-}\) and (**d**) PO\({}_{4}\)\({}^{3-}\) consumption _for Monoraphidium sp._ cultivated in digestate diluted at 1:20 (L 20), 1:30 (L30) and 1:50 (L 50).