Muscat: A research project titled ‘Operational modifications of a full-scale experimental vertical flow constructed wetland with effluent recirculation to optimise total nitrogen removal’ by principal investigator Dr Buthaina al Wahaibi was among the 13 winning projects at the 8th National Research Award.
The award was organised by the Ministry of Higher Education, Research and Innovation. The project won in the category of Environmental and Biological Resources field.
Dr Buthaina al Wahaibi from Oman Water and Wastewater Services Company (OWWSC) said that adequate water and wastewater management is essential for human health, protecting water sources and the environment from pollution. Hence, the treated water to be utilised in water-scarce arid regions as an unconventional source in order to reduce the stress on the consumption of potable water and subsequently contribute to economic growth.
She elaborated that wastewater management strategies can be categorised as centralised or decentralised. Centralised wastewater collection and treatment techniques are costly to build and operate, specifically in areas with low population densities and dispersed communities.
On the other hand, the decentralised approach to wastewater treatment employing a combination of on-site and/or cluster systems is gaining more attention. The decentralised system offers advantages both in terms of operational simplicity and cost effectiveness without the central collection network. The key principles of the decentralised system assumed to be flexible treatment technologies, minimal solids handling, and disposal and/or reuse the treated water locally.
The objective of this study, according to Dr Buthaina, was to evaluate the performance of a two-stage vertical flow constructed wetland (VFCW) for wastewater treatment to be considered as a sustainable, environmental and economic decentralised solution.
Dr Buthaina and her team designed, built and operated a full-scale VFCW to provide a sustainable wastewater treatment solution within the Middle Eastern context. The VFCW had two stages (vertical flow 1 and 2; called VF1 and VF2, respectively) with a total treatment area of 995 m2 and was planted with common reeds (Phragmites australis), while the treated effluent was recirculated to an anoxic tank.
Dr Buthaina explained that the study was divided into two phases: the first phase (Baseline) aimed at evaluating the treatment performance, and the second phase (Modification) aimed at testing different operational modifications to optimise the total nitrogen removal and deal with the nitrified treated effluent.
Samples were collected at the inlet buffer tank and VF2 outlet daily during the first phase and weekly during the second phase. Overall, high removal rates obtained for total suspended solids (TSS) (99.6 per cent), biological oxygen demand (BOD) (98.7 per cent), chemical oxygen demand (COD) (97.8 per cent), ammonia nitrogen (NH3-N) (99.5 per cent), total phosphorus (TP) (97.2 per cent), and pathogens (FC) (99.9 per cent) complied with the Oman Irrigation Standard A.
Dr Buthaina added that the second study aimed to compare the performance of VFCW with well-established membrane bioreactor (MBR) technology. The emphases of the project were to characterise the strength of raw sewage that received identically for two plants, compare the quality of treated effluent to standard and calculate the removal performance. Further, areal and volumetric mass removal rates and percentage removal were analysed as the second approach to assess the system efficiency. The obtained results showed that raw sewage has been categorised as high strength concentration as partially nondomestic wastewater (industrial effluents) received by tankers.
Both technologies produce excellent quality of treated effluent since most parameters showed compliance with Standard A. The removal efficiency achieved at VFCW for BOD, TSS, and TN are 98.68 per cent, 99.57 per cent and 82.98 per cent respectively, while that accomplished at MBR are 98.77 per cent, 98.78 per cent and 96.80 per cent respectively. Thus, the VFCW was proven its capability of pollutants removal as efficient as the MBR. — ONA
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