Summary

Three algal species, Tetradesmus nygaardi (MZ801740), Scenedesmus quadricauda (MZ801741) and Coelastrella sp. (MZ801742), with two species of fungi Aspergillus niger (ATCC 16404) and Candida albicans (ATCC 10231), were used for remediation of heavy metals and water quality improvement as biological approach, The wastewater samples collected from Dhahiba village near Erbil wastewater channel. The river receiving the effluent from Erbil wastewater channel. The mean depth and width of river about 4m and 35m respectively. Both river sides displayed woody riparian vegetation. Wastewater parameters were analyzed by using standard methods.

The parameters mean value before treatment (control, 1 day) by using three doses of microalgal powder (0.2g. l^-1, 1g. l^–1, and 2g. l^-1) were as follows: water temperature, pH EC, TDS, BOD₅, PO₄, NH₄, NO₃ and NO₂ were (22.5 ºC, 8.09, 912 µS.cm^-1, 668 mg. l^-1, 775 mg. l^-1, 23.7 mg. l^-1, 48.2 mg. l^-1, 42.2 mg. l^-1 and 8.94 mg. l^-1) respectively. While Ca, Mg, Na and K were (91.19, 51.03, 152 and 9.9 mg. l^-1) respectively.  

The mean values of parameters water temperature, pH, TDS, EC, BOD₅, PO₄, NH₄, NO₃ and NO₂ before treatment (control,1 day) by using fungi were (22 ºC, 8.2, 823 µS.cm^-1, 487.2 mg. l^-1, 982 mg. l^-1, 29.7 mg. l^-1, 76.05 mg. l^-1, 68.27 mg. l^-1 and 21.78 mg. l^-1) respectively. Whereas the mean value of Ca, Mg, Na and K were (176.3, 53.89, 117.7 and 15 mg. l^-1) respectively.

Results of the physicochemical parameters showed that during the treatment period (21 days) in all bioreactors (microalgae, fungi and microbial mixed strains) that Statistically there were a significant different (P≤0.05) between treatments and the control during study period.

According to the obtained results during the treatment period in all experimental bioreactors of microalgae, fungi and microbial mixed cultures the pH and water temperature of wastewater increased continuously and reached the maximum range of (8.62 and 28ºC) respectively. In contrast, the results indicated that maximum remediation of EC and TDS occur at highest applied dose (2g. l^-1) were (61.5, 62.4 and 61.3%) for EC and (73.9, 75.3 and 73.3%) for TDS at concentration (2g.l^-1) respectively by using microalgae T. nygaardi. S. quadricauda and Coelastrella sp., Whereas maximum removal among by fungus was showed by Aspergillus niger were reduced EC and TDS by (78.49 %79.78%) respectively. Furthermore, the maximum remediation among microbial mixed culture shown by A. niger with C. albicans were (81.65, 81.52%) on day 21 of the study.

Contrasting to the other parameters, the maximum remediation of BOD₅ concentration was recorded at the lowest applied dose of (0.2g. l^-1), additionally microalga S. quadricauda had the highest potential in removing BOD5 for all doses (93.54, 91.93 and 90.32%) respectively. While A. niger has the higher efficiency in removing BOD₅ that removed 87.27%, additionally the percent remediation of BOD₅ was 94.9% by mixed culture of S. quadricauda with A. niger.

Consequently, the highest PO₄ reduction by using microalgal species noted at the highest applied dose 2 g. l^-1 were (93.56, 93.83 and 93.14%) respectively, Besides the fungus C. albicans removed 91.58% of PO₄, additionally the highest removal among bioreactors of microbial mixed culture indicated by S. quadricauda with T. nygaardi which reduced PO₄ by 94.94%.

Therefore, the maximum potential of T. nygaardi, S. quadricauda and Coelastrella sp. to remove NH₄ reported at dose (2g.l^-1) were (96.7, 97 and 96.6%) respectively. On the other hand, A. niger had the higher efficiency in reduction of NH₄ (89.57 %), Furthermore, a pure mixed culture of S. quadricauda with T. nygaardi decreased NH₄ by (90.73%) respectively on the same time of period

Moreover, three microalgae species at the highest applied dose (2g.l^-1) decreased NO₃ and NO₂ by (85.5, 86 and 83.9%) and (85.45,86.01 and 93.84%) respectively. While, A. niger showed the higher potential in remediation of NO₃ which reduced by 83.52%. Whereas the highest removal of NO₂ was recorded by Candida albicans during study period was (88.98%). Additionally, the mixed culture of S. quadricauda with T. nygaardi remediate NO₃ and NO₂ by (88.23 and 93.84%) respectively.

In addition, the result showed that the chlorophyll a content reached the maximum values on the 17^th day of the experiment in all reaction batches of (0.2, 1 and 2 g.l^-1) for all microalgal species and reached (1.102, 1.167 and 1.517 mg. l^-1) for T. nygaardi and (1.130, 1.200 and 1.522 mg. l^-1) for S. quadricauda and (0.987, 1.087 and 1.434 mg. l^-1) for Coelastrella sp. Whereas the concentration of chlorophyll a during nutrient removal by pure mixed cultures of S. quadricauda with A. niger, S. quadricauda with C. albicans and S. quadricauda with T. nygaardi was increased and reached the highest value (1.052, 1.005 and 2.521 mg. l^-1) respectively on day 21^st of study.

In term of heavy metals, three algae species, T. nygaardi, S. quadricauda and Coelastrella sp., with two fungi species, Aspergillus niger and Candida albicans, were used for remediation of heavy metals (Pb and Cd) for 20 days. The mean value of heavy metals (Pb and Cd) were (5, 15, 35 and 50ppm) before treatment (control).

Generally, the obtained results revealed that the maximum remediation for all concentrations of Pb (5, 15, 35 and 50ppm) observed on day 20^th of the experiment and at the lowest applied concentration 5ppm by using microbial strains (single and mixed). Statistically there were a significant different (P≤0.05) between treatments and the control during study period of 20 days. At the lowest applied concentration of Pb (5ppm), microalgae (T. nygaardi, S. quadricauda and Coelastrella sp. removed Pb by (83.80, 80 and 86.8%), On the other hand, A. niger and C. candida reduced Pb at the lowest applied concentration were (85.8 and 84.2%), While the microbial mixed cultures remediate the Pb by (94, 90, 86.28 and 81.6%) respectively.

Coelastrella sp. showed the highest potential in comparison to the other microalgae species for all concentrations of Cadmium were removed by (84, 80.66, 77.14 and 76.94%) respectively. Whereas the fungus A. niger removed Cd by (80, 79.2, 77.71 and 76.85%), additionally the microbial mixed culture of (S. quadricauda with T. nygaardi) showed the highest efficiency in removal of Cd were reduced by (88, 86.66, 84.57 and 79%) for all applied doses of Cd (5, 15, 35 and 50ppm) respectively. The lowest applied dose of cadmium (5ppm) had the highest remediation percent among all microbial strains (single and mixed).

The results showed that the concentration of chlorophyll a in microalgae species increased with increasing the concentrations of Pb. The microalgal strains T. nygardi, S. quadricauda and Coelastrella sp. chlorophyll a reached (4.94, 4.88 and 4.99 mg. l^-1) respectively at 50ppm of pb. In contrast the chlorophyll a content in a bioreactor of Cd has the highest rate at the lowest applied concentration (5ppm) were (3.67, 3.63 and 3.74 mg. l^-1) respectively, on day 16^th of the experiment.

          Chlorophyll a content in microalgae species among pure mixed microbial strains (S. quadricauda with A. niger, S. quadricauda with C. albicand and S. quadricauda with T. nygaardi) reached the maximum values (3.15, 3.03 and 5.77 mg. l^-1) for Pb and (1.81, 1.64 and 5.324 mg. l^-1) for Cd on the same time. The obtained result indicated that highest reduction of Pb and Cd was recorded on day 20^th of the experiment for all concentrations in all reaction batches by using microalgae and fungi. The lowest applied concentration of Pb and Cd has the highest removal percent.