Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes.

Barbara Krystyna Wilk,Sylwia Fudala-Ksiazek,Ewa Siedlecka,Aneta Luczkiewicz,Małgorzata Szopińska,Michał Sobaszek

doi:10.3390/ma14174971

Barbara Krystyna Wilk, Sylwia Fudala-Ksiazek + Show 4 more

Open Access

https://doi.org/10.3390/ma14174971

Copy DOI

Abstract

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH4+ (2069 ± 103 mg·L−1), chemical oxygen demand (COD) (3608 ± 123 mg·L−1), high salinity (2690 ± 70 mg Cl−·L−1, 1353 ± 70 mg SO42−·L−1), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm−2 was the most effective amongst those tested (C8h/C0: COD = 0.09 ± 0.14 mg·L−1, N-NH4+ = 0.39 ± 0.05 mg·L−1). COD removal fits the model of pseudo-first-order reactions and N-NH4+ removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm−2) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m−3 (BDD 0.5 k, j = 100 mA·cm−2).

Highlights

Despite a new solid waste strategy and enhanced recycling and utilization, landfilling still represents an important path for municipal solid waste management
In the case of highly boron-doped 15 k, the grain size decreased to approximately 0.5 μm
The results showed that high values of the applied j caused elimination of N-NH4 + with zeroth-order kinetics, whereas, using low values of the applied j, exponential-like decaying ammonia concentration curves were obtained

Summary

Introduction

Despite a new solid waste strategy and enhanced recycling and utilization, landfilling still represents an important path for municipal solid waste management. LLs from new cells (1–2 years old) usually have higher concentrations of biodegradable contaminants (ratio of five-day Biochemical Oxygen Demand to Chemical Oxygen Demand, BOD5 /COD) ratio is >0.5) due to the high concentration of volatile organics) [4,5]. LLs generated by older cells (>10 years old) are usually less prone to biological degradation with BOD5 /COD < 0.3 (due to the high concentration of refractory organic matter) [6]. The appropriate BOD5 /COD ratio itself does not ensure good biochemical degradation of contaminants [7]. The problem of efficient and economically viable treatment of LLs is one of the crucial, still-unresolved environmental issues globally

Objectives

Methods

Results

Conclusion