Vertical subsurface flow constructed wetlands for the removal of petroleum contaminants from secondary refinery effluent at the Kaduna refining plant (Kaduna, Nigeria).

Typha latifolia-planted vertical subsurface flow constructed wetlands (VSSF CWs) and an unplanted microcosm constructed wetland were used for treating secondary refinery wastewater from the Kaduna Refining and Petrochemical Company (KRPC, Nigeria). Cow dung was applied to the planted wetlands at the start of the experiment and after 3 months to enhance plant growth and petroleum degradation. The T. latifolia-planted VSSF CWs removed 45-99% total petroleum hydrocarbon (TPH), 99-100% phenol, 70-80% oil and grease, 45-91% chemical oxygen demand (COD), and 46-88% total suspended solids (TSSs). The performance of the unplanted control VSSF CW achieved lower removal efficiencies (15-58% TPH, 86-91% phenol, 16-44% oil and grease, 24-66% COD, and 20-55% TSS). T. latifolia plants had a bioaccumulation factor (BAF) > 1 for phenol, total nitrogen (TN), and total phosphate (TP), suggesting a high removal performance for these contaminants and good translocation ability (TF) for TPH, phenol, oil and grease, and TN, with the exception of TP which was mainly retained in their roots (BAF = 47). This study showed T. latifolia is a good candidate plant to be used in VSSF CWs for polishing secondary refinery wastewater in developing countries.

Performance evaluation of duplex constructed wetlands for the treatment of diesel contaminated wastewater.

A duplex constructed wetland (duplex-CW) is a hybrid system that combines a vertical flow (VF) CW as a first stage with a horizontal flow filter (HFF) as a second stage for a more efficient wastewater treatment as compared to traditional constructed wetlands. This study evaluated the potential of the hybrid CW system to treat influent wastewater containing diesel range organic compounds varying from C7 - C40 using a series of 12-week practical and numerical experiments under controlled conditions in a greenhouse (pH was kept at 7.0 ±â€¯0.2, temperature between 20 and 23° C and light intensity between 85 and 100-µmol photons m-2 sec-1 for 16 h d-1). The VF CWs were planted with Phragmites australis and were spiked with different concentrations of NH4+-N (10, 30 and 60 mg/L) and PO43--P (3, 6 and 12 mg/L) to analyse their effects on the degradation of the supplied petroleum hydrocarbons. The removal rate of the diesel range organics considering the different NH4+-N and PO43--P concentrations were simulated using Monod degradation kinetics. The simulated results compared well with the observed database. The results showed that the model can effectively be used to predict biochemical transformation and degradation of diesel range organic compounds along with nutrient amendment in duplex constructed wetlands.

Fate of heavy metals in vertical subsurface flow constructed wetlands treating secondary treated petroleum refinery wastewater in Kaduna, Nigeria.

This study examined the performance of pilot-scale vertical subsurface flow constructed wetlands (VSF-CWs) planted with three indigenous plants, i.e. Typha latifolia, Cyperus alternifolius, and Cynodon dactylon, in removing heavy metals from secondary treated refinery wastewater under tropical conditions. The T. latifolia-planted VSF-CW had the best heavy metal removal performance, followed by the Cyperus alternifolius-planted VSF-CW and then the Cynodon dactylon-planted VSF-CW. The data indicated that Cu, Cr, Zn, Pb, Cd, and Fe were accumulated in the plants at all the three VSF-CWs. However, the accumulation of the heavy metals in the plants accounted for only a rather small fraction (0.09-16%) of the overall heavy metal removal by the wetlands. The plant roots accumulated the highest amount of heavy metals, followed by the leaves, and then the stem. Cr and Fe were mainly retained in the roots of T. latifolia, Cyperus alternifolius, and Cynodon dactylon (TF < 1), meaning that Cr and Fe were only partially transported to the leaves of these plants. This study showed that VSF-CWs planted with T. latifolia, Cyperus Alternifolius, and Cynodon dactylon can be used for the large-scale removal of heavy metals from secondary refinery wastewater.