ABSTRACT
The reuse of treated wastewater for agriculture and other purposes is globally recognized as a reliable water source. Constructed wetlands are cost-effective and reliable green technologies for wastewater treatment, offering an environmentally friendly and affordable solution with minimal operational and maintenance requirements. This study assessed four wetland technologies (HFWSF, VFSF, VSSF, and HSSF) for treating greywater according to regulatory standards. The technologies effectively maintained pH levels, and both treated and untreated greywater samples met FEPA limits. They efficiently reduced dissolved and suspended particles, remaining below FEPA discharge limits for conductivity, TDS, turbidity, and TSS. However, elevated ammonia levels in both treated and untreated samples required additional treatment or mitigation. Sulphate levels were successfully mitigated, and phosphorus limits were met, with HFWSF already compliant even before treatment. Nitrate levels were reduced to meet FEPA limits, ensuring regulatory compliance. While BOD limits were met in both treated and untreated samples, untreated samples exceeded COD limits, necessitating more efficient treatment methods. HFWSF and HSSF complied with COD limits, whereas VFSF and VSSF did not. Both treated and untreated samples exceeded FEPA limits for oil and grease, indicating the need for additional treatment. Untreated samples exhibited high coliform contamination levels, underscoring the importance of effective treatment. However, all technologies successfully reduced coliform levels in treated samples, meeting FEPA limits and confirming treatment effectiveness. The combination of Typha (Domingensis) in the horizontal subsurface flow constructed wetland improved pollutant removal, nutrient removal, and contaminant elimination. Incorporating water Hyacinth (Eichhornia crassipes) with horizontal free water surface flow wetland technology demonstrated the highest efficacy in removing various pollutants. This combination outperformed other wetland technologies in effectively removing pollutants, including ammonia (60%), oil and grease (78.46%), COD (85%), TP (37.04%), FC (75%), and TC (79.59%), representing significant progress in greywater treatment.
ABSTRACT
Carwash stations use large volumes of water and release harmful chemicals into the environment through their operations. While a significant body of literature has focused on exploring water use in the carwash industry, none has provided comprehensive information on both the pollution loads of the wastewater emanating from this industry and water consumption. Understanding how much water is used and the pollution loads of wastewater from this industry is useful to ensure adoption of water conservation measures and design wastewater recycling systems given the dwindling freshwater resources globally. This study estimated the freshwater quantities used to wash different vehicle types and the pollution loads of the resulting wastewater in the Kumasi Metropolis. Seven proxy carwash stations were purposively selected and monitored to estimate the water used to wash six different categories of vehicles. Composite wastewater samples from three carwash stations were analysed for concentrations of different contaminants which were used to compute pollution loads. Using R software, one-way ANOVA with Tukey's (HSD) post-hoc testing and 2-sample t-test at 95% confidence interval were employed to test statistical differences. After an 8-week monitoring campaign involving 3,667 vehicles, the study showed that average water used for each vehicle type were in the order: Motorbike - 97L (95% CI: 90-103L); Salon car - 158L (95% CI: 154-161L); SUV - 197L (95% CI:191-203L); Buses/Coaches - 370L (95%CI:351-381L); Articulated truck 1,139L (95% CI:916-1,363L); Graders/Loaders - 1405L (95% CI:327-2,483L). Overall, the carwash industry in the Metropolis uses about 1000m3 of freshwater daily and discharges the resulting wastewater into waterways untreated. The wastewater has a low Biodegradability Index (0.3-0.4) and is characterized by a mildly alkali pH (7.6-8.6) with high levels of Sulphates (40.8-69.8 mg/L), COD (990-1413 mg/L), TSS (1260-3417 mg/L) and E. coli (2.3-4.7 × 103 CFU/100mL). Pollution loads of BOD and COD were up to 2tons/year and 6tons/year respectively. Stipulated effluent discharge guideline values were mostly exceeded - in some cases by up to 68 times. To avert the unbridled wastage of freshwater, the study recommends enforcement of wastewater recycling for all carwash stations and promulgation of a tax system that rewards stations that recycle wastewater and surchages those wasting freshwater.
ABSTRACT
This study assessed the contaminant removal potential of a low-cost alum synthesized from bauxite slime waste compared to industrial grade alum [Al2(SO4)3.18H2O] in treating car wash wastewater using standard jar tests. The synthesized alum was subsequently applied as a coagulant to test the short-term performance of a bench scale flocculation-flotation system for treating car wash wastewater. Coagulant dosages and mixing intensities were optimized for both coagulants and differences were analyzed with R using two-way ANOVA with Tukey's (HSD) post hoc testing. Per the jar tests, percentage removal of up to 99%, 34%, and 75% of turbidity, anionic surfactants (AS), and COD, respectively, was achieved with 90 mg/L of the synthesized alum compared to 100%, 37%, and 74% for industrial grade alum. Contaminant removal efficiencies of both coagulants were comparable (p > 0.05). However, coagulant dosage strongly influenced the removal of turbidity, AS, and COD (p < 0.05) while mixing intensity influenced all but COD. The bench-scale flocculation-flotation system completely removed turbidity (100%) and reduced AS and COD by up to 92% and 99% respectively. The results of this study demonstrate the potential of alum synthesized from bauxite slime waste as a cheaper alternative for industrial grade alum in wastewater recycling for the car wash industry.
