Ammoniacal nitrogen and organics removal modelling in vertical flow wetlands treating strong wastewaters

This paper reports a comparative evaluation between 2 kinetic models for predicting nitrification and biodegradable organics (BOD5) removal rates in 5 vertical flow (VF) wetland systems, that received strong wastewaters (i.e. tannery, textile and municipal effluents). The models were formulated by combining first order and Monod kinetics, with continuous-stirred tank reactor (CSTR) flow approach. The performance of the 2 models had been evaluated with 3 statistical parameters: coefficient of determination (R2), relative root mean square error (RRMSE), and model efficiency (ME). The statistical parameters indicated better performance of the Monod CSTR model (over first order CSTR approach), for correlating ammoniacal nitrogen (NH4—N) and BOD5 removal profiles across VF systems. Higher Monod coefficient values (from Monod CSTR model) coincided with greater input NH4—N and BOD5 loading, and experimentally measured removal rate (g/(m2·d)) values. Such trends indicate that NH4—N and BOD5 removals in the VF systems were mainly achieved via biological routes. On the other hand, the rate constants (from the first order CSTR model) did not exhibit such correlations (of Monod coefficients), elucidating their inefficiencies in capturing overall removal mechanisms. The interference of organics removal on nitrification process (in VF wetlands) was identified through Monod coefficients. The deviation between NH4—N and BOD5 Monod coefficients imply incorporation of both coefficients, for calculating the area of a single VF bed. Overall, closer performance of the Monod CSTR model for predicting NH4—N and BOD5 removals indicate its potential application, as a design tool for VF systems