Suiliang Huang

Processes impacting on benzene removal in vertical-flow constructed wetlands.

The overall aim of this research project was to reduce low molecular weight hydrocarbons such as benzene in produced wastewaters. Over 30 months of research was conducted to test the treatment performance in terms of benzene removal in vertical-flow constructed wetlands. Based on an influent concentration of 1 g L(-1) benzene, the results show mean benzene removal efficiencies between 88.71% and 89.77%, and 72.66% and 80.46% for indoor and outdoor constructed wetlands, respectively. A statistical analysis indicated that the five days at 20 degrees C N-allylthiourea biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), nitrate-nitrogen (NO(3)-N), dissolved oxygen (DO) and electric conductivity (EC) values of the effluent were positively correlated with the effluent benzene concentrations following the order COD>DO>EC>NO(3)-N>BOD(5), and negatively correlated according to the order pH>redox potential (redox)>temperature (T)>turbidity. No strong relationships between benzene and the variables ortho-phosphate-phosphorus (PO(4)(3-)) and ammonia-nitrogen (NH(4)-N) were recorded.

Nutrient distribution within and release from the contaminated sediment of Haihe River

We assessed nutrient characteristics, distributions and fractions within the disturbed and undisturbed sediments at four sampling sites within the mainstream of Haihe River. The river sediments contained mostly sand (> 60%). The fraction of clay was < 3%. Total nitrogen (TN) and total phosphorus (TP) concentrations ranged from 729 to 1922 mg/kg and from 692 to 1388 mg/kg, respectively. Nutrient concentrations within the sediments usually decreased with increasing depth. The TN and TP concentrations within the fine sand were higher than for that within silt. Sediment phosphorus fractions were between 2.99% and 3.37% Ex-P (exchangeable phosphorus), 7.89% and 13.71% Fe/Al-P (Fe, Al oxides bound phosphorus), 61.32% and 70.14% Ca-P (calcium-bound phosphorus), and 17.03% and 22.04% Org-P (organic phosphorus). Nitrogen and phosphorus release from sediment could lead to the presence of 21.02 mg N/L and 3.10 mg P/L within the water column. A river restoration project should address the sediment nutrient stock.

Nutrient removal as a function of benzene supply within vertical-flow constructed wetlands

The role of benzene, macrophytes and temperature in terms of nutrient removal within constructed wetlands is unknown. Therefore, a research study over approximately 30 months was conducted to assess the potential of vertical‐flow constructed wetlands to treat nutrients and to examine the effect of benzene concentration, presence of Phragmites australis (Cav.) Trin. ex Steud (common reed), and temperature control on nutrient removal. Experimental wetlands removed between 72% and 90% of benzene at an influent concentration of 1000 mg L−1. A statistical analysis indicated that benzene is linked to increased effluent chemical oxygen demand and biochemical oxygen demand concentrations. However, there was no significant relationship between benzene treatment and both nitrogen and phosphorus removal. Phragmites australis played a negligible role in organic matter (chemical oxygen demand, biochemical oxygen demand, nitrogen and phosphorus) removal. Control of temperature favoured biochemical oxygen demand removal. However, no significant difference in chemical oxygen demand, and nitrogen and phosphorus removal was detected. Only the combination of the benzene and temperature variables had a significant impact on biochemical oxygen demand removal. The effluent biochemical oxygen demand concentrations in temperature‐controlled benzene treatment wetlands were much lower than those located in the natural environment. However, any other combination between benzene, P. australis and the environmental control variables had no significant effect on biochemical oxygen demand, chemical oxygen demand, or nitrogen and phosphorus removal.

Nutrient removal in vertical subsurface flow constructed wetlands treating eutrophic river water

Four planted (Typha latifolia L.) pilot-scale vertical subsurface flow constructed wetlands were constructed to purify the eutrophic water of the Jinhe River in Tianjin (China) and to determine the feasibility of constructing a full-scale system in the future. The effects of intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on the nutrient removal potential were also evaluated. During the entire running period, supplementary aeration enhanced the chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus first order mean removal constants by 0.28 m/d, 3.05 m/d, 0.92 m/d, 0.74 m/d and 0.60 m/d, respectively, but reduced the nitrate-nitrogen removal constant by 1.72 m/d in contrast to non-aerated wetlands. A significantly positive contribution of PHPB to nutrient removal was obtained. The combination of artificial aeration and PHPB resulted in the augmentation of the first order mean removal constants by 0.29 m/d, 3.12 m/d, 1.15 m/d, 0.65 m/d and 0.54 m/d for chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus, respectively. Findings from a brief cost-benefit analysis suggest that both artificial aeration and the presence of PHPB would result in enhanced nutrient removal that is cost efficient for future projects, particularly if electricity costs are low.

Laboratory analyses of nutrient release processes from Haihe River sediment

Abstract Sediment samples were collected from the heavily contaminated Haihe River to conduct static nutrient release experiments with tap water, and to evaluate the effect of dredging depths, salinity and light on the corresponding release processes. The study is significant because it helps decision-makers to assess the likely impact of dredging (e.g. eutrophication) on contaminated freshwater and brackish rivers. The concentrations of total nitrogen and inorganic phosphorus were approximately 950 mg/kg and 760 mg/kg, respectively. The typical organic matter concentration was 8.6%. Data obtained from the nutrient leaching experiments indicated that 5cm-dredging of sediment reduced the water column total phosphorus, total dissolved phosphorus and ammonia-nitrogen concentrations insignificantly. In contrast, dredging 10cm surface sediment could improve the water quality. Higher salinity values benefited the release of nitrogen and phosphorus from sediment. In contrast to indoor experiments, concentrations of total phosphorus, total dissolved phosphorus and ammonia-nitrogen were higher for the outdoor experiments.