Background High-strength wastewater defined by elevated levels of hazardous pollutants measured in BOD, heavy metals, nutrients and other toxic substances. This kind of wastewater discharged to water body without treatment from different industrial sectors that adversely affects aquatic environment and downstream water consumers. The general objective of this study is to investigate efficient substrate with selected plant type for constructed wetland to remove hazardous pollutants from tannery wastewater. This study was conducted at Modjo town, Modjo tannery PLC. Plug flow experimental study design was carried out. The substrate (Pumice) was collected around the study area and chemical characteristics were determined. Chrysopogon zizanioides was planted and grown for 5 months before running tannery wastewater for the treatment. The composite wastewater was introduced to the constructed wetland from Modjo leather industry, Ethiopia. The physicochemical analysis of the sample wastewater was done before and after treatment at four different hydraulic retention time. Results Characterization of the untreated tannery wastewater revealed that the mean concentration of BOD5, COD, TSS, PO4-P, TP, NO3-N, TN and total chromium were 1641 ± 373.6, 6953.33 ± 339.4, 1868 ± 863.1, 88.06 ± 40.8, 144.53 ± 20.8, 116.66 ± 26.6, 650.33 ± 93.6 and 18.33 ± 6.7 mg/l respectively beyond the permissible limits. The maximum removal efficiency of the constructed wetland in pumice bed revealed that BOD5 at HRT 7and 9 days (96.42%, 96.30%), COD at HRT 5 and 7 days (96.76%, 96.91%), NO3-N at HRT 5 and 7 days (99.99%, 99.68%), TN (98.67%, 99.00%), PO4-P HRT 7and 9 days (96.97%,100%), TP at HRT 5 and 7 days (94.79%, 96.17%) and total Chromium at HRT 5 and 7 days (98.36%, 98.91%) respectively. Whereas, the removal efficiency of constructed wetland bed with gravel substrate used as a control subject with similar condition to pumice showed lower performance. The result between pumice and gravel bed was tested for their significance difference using two sample t-test statistics. Based on the test statistics, the pumice substrate perform better than the gravel significantly at 95% confidence interval, p-value = 0.01. Conclusion Pumice substrate and Chrysopogon zizanioides have a potential ability to remove hazardous pollutants from tannery wastewater in horizontal subsurface constructed wetlands.
Background The combination of nutrient removal using microalgae from wastewater with carbohydrate production has been considered as a promising approach for sustainable wastewater treatment and production of valuable products such as biofuels. In Ethiopia, urbanization and industrial development are not in tandem with wastewater treatment system The objective of this study was to evaluate nutrient removal and carbohydrate production potential of the indigenous microalgae Scenedesmus sp. grown in anaerobically digested brewery wastewater. The indigenous Scenedesmus sp. was grown in an anaerobically digested brewery effluent in different seasons of the year. The biomass was converted into carbohydrate using microwave, autoclave, and oven as pretreatment, followed by optimization for acid concentrations and hydrolysis time. Result The overall removal efficiencies for the indigenous Scenedesmus sp. based wastewater treatment system were over 99%, 92%, 63%, 65% and 75% for NH4+-N, TN, PO43− -P, TP and COD, respectively. The concentrations of final effluent quality of these parameters except for phosphorus nutrient were below the permissible discharge limit for brewery effluent standard set by Ethiopian Environmental Protection Authority. With regard to carbohydrate production, microwave-assisted acid hydrolysis with HCl produced a higher total sugar than that of autoclave and oven pretreatments. Among acid concentrations, HCl with 3 N produced a higher total sugar, which is significantly different (P < 0.05) to the other acid concentrations. The highest total sugar (233.89 mg g−1) was obtained from microalgal biomass during the 20 min hydrolysis time with 3 N HCl and 5% (w/v) biomass at 1000 watts and 1200C. Conclusions This study showed that there is an opportunity for using the indigenous microalgae for sustainable wastewater treatment and for carbohydrate production that uses as bioethanol source in Ethiopia.
The use of wastewater as a nutrient source for microalgae cultivation is considered as a cost-effective approach for algal biomass and biofuel production. The microalgal biomass contains carbohydrates that can be processed into bioethanol through different extraction methods. The objective of this study is to optimize the microwave-assisted extraction (MAE) of carbohydrates from the indigenous Scenedesmus sp. grown on brewery effluent. Optimization of independent variables, such as acid concentration (0.1–5 N), microwave power (800–1200 W), temperature (80–180 °C) and extraction time (5–30 min) performed by response surface methodology. It was found that all independent variables had a significant and positive effect on microwave-assisted carbohydrate extraction. The quadratic model developed on the basis of carbohydrate yield had F value of 112.05 with P < 0.05, indicating that the model was significant to predict the carbohydrate yield. The model had a high value of R 2 (0.9899) and adjusted R 2 (0.9811), indicating that the fitted model displayed a good agreement between the predicted and actual carbohydrate yield. An optimum carbohydrate yield obtained was 260.54 mg g −1 under the optimum conditions of acid concentration (2.8 N), microwave power (1075 W), temperature (151 °C) and extraction time (22 min). The validation test showed that the model has adequately described the microwave-assisted extraction (MAE) of carbohydrates from microalgal biomass. This study demonstrated that the indigenous Scenedesmus sp. grown on brewery effluent provides a promising result in carbohydrate production for bioethanol feedstock.
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