Release Mechanism, Secondary Pollutants and Denitrification Performance Comparison of Six Kinds of Agricultural Wastes as Solid Carbon Sources for Nitrate Removal.

Yu Ling,Yang Chang,Congyu Li,Weiyang Dong,Haiyan Wang,Huan Wang,Ming Chang,Guokai Yan

doi:10.3390/ijerph18031232

Abstract

Agricultural wastes used as denitrification carbon sources have some drawbacks such as excessive organic carbon release and unclear release characteristics of nitrogen, phosphorus, and chromatic substances, which can cause adverse effects on the effluent quality during the denitrification process. The composition and surface characteristics, carbon release mechanisms, and secondary pollutant release properties of six kinds of agricultural wastes, i.e., rice straw (RS), wheat straw (WS), corn stalk (CS), corncob (CC), soybean stalk (SS), and soybean hull (SH) were studied and analyzed in this research. The denitrification performance of these agricultural wastes was also investigated extensively by batch experiments. The results showed that the carbon release basically followed the second-order reaction kinetic equation and Ritger–Peppas equation in the 120 h reaction, and it was mainly controlled by the diffusion process. The kinetic equation fitting results and bioavailability test suggested that the potential risk of excessive effluent COD of CC was the lowest due to the appropriate amount and degradability of its released carbon. The NH4+-N, TN, and TP in the leachate of RS were higher than those of the other five agriculture wastes, and the chroma in the leachate of WS and CS was heavier than that of the others. CC released the lowest pollutants, which resulted in slight fluctuations of effluent quality in the start-up period (1–11 d), and it had the best nitrogen removal capacity in the denitrification experiment. The average NO3−-N removal of CC was 5.12 mg for each batch in the stable period (11–27 d), which was higher than that of others, and less NO2−-N, NH4+-N, and COD were accumulated in the CC effluent during the whole denitrification process.

Highlights

Nitrogen pollution has become a severe issue due to rapid socio-economic development [1]
Heterotrophic denitrification, which utilizes organic carbon sources as electron donors, has higher denitrification rates compared with autotrophic denitrification [4]
The deficiency of available carbon sources is an intractable problem for heterotrophic denitrification in the treatment

Summary

Introduction

Nitrogen pollution has become a severe issue due to rapid socio-economic development [1]. Large amounts of nitrogen compounds are discharged into the water due to excessive fertilizer application and domestic and industrial discharge [2]. Excessive nitrogen can cause serious environmental problems, such as the as eutrophication of rivers and lakes and the deterioration of water sources, and influence human health [3]. Nitrogen removal from water and wastewater is important for environmental and human health protection. Among all the nitrogen removal methods and technologies, biological denitrification is generally applied due to its high efficiency and low cost. Heterotrophic denitrification, which utilizes organic carbon sources as electron donors, has higher denitrification rates compared with autotrophic denitrification [4]. The deficiency of available carbon sources is an intractable problem for heterotrophic denitrification in the treatment

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Conclusion