Corn Straw as a Solid Carbon Source for the Treatment of Agricultural Drainage Water in Horizontal Subsurface Flow Constructed Wetlands

Abstract

Agricultural drainage water with a low C/N ratio restricts the nitrogen and phosphorus removal efficiencies of constructed wetlands. Thus, there is a need to add external carbon sources to drive the nitrogen and phosphorus removal. In this study, the effects of the addition of corn straw pretreated with different methods (acid treatment, alkali treatment, and comminution) on treating agricultural drainage water with a low C/N ratio were investigated in constructed wetlands. The results showed that soaking the corn straw in an alkaline solution was the most suitable pretreatment method according to the release rule of chemical oxygen demand (COD) and the dissolution of total nitrogen (TN) and total phosphorus (TP). The average removal efficiency of TN and TP in constructed wetlands increased respectively by 37.2% and 30.5% after adding corn straw, and by 17.1% and 11.7% after adding sodium acetate when the hydraulic retention time (HRT) was 3 days. As an external carbon source, straw was cheap, renewable, and available. In contrast, the sodium acetate demanded high costs in a long-term operation. Therefore, corn straw had a great advantage in treatment effect and cost, which improved the treatment efficiency of agricultural drainage water using a byproduct of agricultural production as a slow-release carbon source.

Enhanced Nutrients Removal Using Reeds Straw as Carbon Source in a Laboratory Scale Constructed Wetland

“…Therefore, the results from the current study provided confidence that the reeds straw addition could be a good strategy and technical solution for low C/N wastewater treatment, by a considerable enhancement of TN and TP removal of 59.7% and 35.0%, respectively, at HRT of four days. Although it was questionable to compare this enhancement with other cases of different materials being added and the varied operation condition, as well as different CW system configuration, the enhancement was comparable from the limited literature, 37.2% for TN and 30.5% for TP [ 12 ]. Chen et al [ 11 ] had concluded that denitrification contributed to 54–94% N removal in CWs.…”

“…The reeds straw were prepared from the harvested mature reeds in the Erhai riparian natural wetland. After exposure outside to dry, the reeds were chopped into 1~2 cm bars and then mixed with the soil [ 12 ]. The total mass of the reed bars was about 9.2 kg with a specific filling quantity of 19.2 kg/m 2 .…”

“…In the first stage (0–28 days) of the continuous operation, an HRT of three days was adopted in order to evaluate the release of the nutrients from the straw. Then, from days 28 to 149 (2nd stage), the impact of the HRT (two days, three days, and four days) [ 12 ] on the pollutant removal was studied by changing the influent flow rate, as depicted in Figure 1 b. The influent was introduced into the CWs using a peristaltic pump, and the effluent overflowed out of the wetland from three drainage ports.…”

“…Chen et al [ 11 ] reported that the Typha latifolia litter addition could greatly improve nitrate removal in subsurface-batch CWs through the continuous input of organic carbon. Li et al [ 12 ] demonstrated the use of corn straw, after pretreatment of soaking the corn straw in an alkaline solution for treating agricultural drainage water with a low C/N ratio in a horizontal subsurface flow CW. The average removal efficiency of TN and TP in tested CW increased by 37.2% and 30.5%, respectively, under the hydraulic retention time (HRT) of three days.…”

Edge-of-Field Technologies for Phosphorus Retention from Agricultural Drainage Discharge

“…Horizontal or vertical subsurface-flow constructed wetlands can be an advantage in relation to SFCWs in regards to smaller area requirements. Li et al [112] demonstrated that five newly constructed experimental horizontal-flow wetlands effectively retained P from agricultural drainage discharge (35%, 38%, 38%, 57% and 31%), which was likely owing to the unsaturated medium with P. The study also demonstrated that the percentage P retention increased after the addition of a carbon source, which probably favored microbial uptake of P, and under longer HRTs. The use of subsurface-flow constructed wetlands, however, is largely restricted to the treatment of wastewater (e.g., sewage) and is less used in agricultural catchments than SFCWs due to high maintenance costs, risk of clogging and limited P sorption capacity of the medium [113].…”