Water temperature effect on the reaction rate constant of pollutants in a constructed wetland for the treatment of swine wastewater

Abstract

Temperature is an important factor in the processes that are carried out in biological systems. In wetlands, the capacity to remove pollutants is limited by environmental factors. The objective was to determine the effect of water temperature on the rate constant for the removal of pollutants in wastewater from pig farms. The evaluation was carried out in a surface flow constructed wetland (SFCW) consisted of a 9 m long and 3 m wide channel covered with a high density geo-membrane (4 mm). The SFCW bed consisted of a 30 cm layer of sand and clay; native vegetation from the study area was used. The hydraulic retention time (HRT) was 10 d, and 12 experimental runs were carried out between January 2014 and December 2015. The results showed an average removal rate of the chemical oxygen demand (COD) of approximately 75 and 74 % for 2014 and 2015 respectively; the average removal rate of ammonia nitrogen (NH3-N) of 65 and 69 %, while the average total nitrogen (TN) removal rate was 69 and 63 % and the total phosphorus (TP) removal rate was 75 and 73 % in 2014 and 2015, respectively. The water temperature along the experimental phase ranged from 13 to 22 °C. The removal of NH3-N showed the highest dependence on water temperature with values of R2 = 0.8787 in 2014 and R2 = 0.8957 in 2015. The volumetric reaction constant (kv d-1) in 2014 ranged from 0.041 to 0.185 d-1 with an average temperature in the wetland of 13 to 21 °C. While k presented an average value of 2.60 cm d-1 in 2014, and in 2015 the observed value was 3.22 cm d-1. It was evident that the value of kv augmented as the water temperature increased, which indicates that this factor has a direct effect on the removal of the NH3-N.