Topics in Current Chemistry (2020) 378:7
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4.3 Industrial Wastewater Treatment and Energy Recovery from Hydrogen
Production
Industrial processes utilize water that can be contaminated by any organic or inorganic compounds used in the process. Thus, the characteristics of urban wastewater are completely different from those of industrial wastewater. The role of AOPs
in industrial wastewater treatment is often to improve its biodegradability and/or
reduce toxicity, before applying a biological process. AOPs can also be used after
biological treatment of industrial wastewater to further reduce residual contaminants
to meet the standards for effluent disposal or reuse. In the following subsections, the
application of HPC to various types of industrial wastewater (food, textile, tanning,
and pharmaceutical/pesticide) are critically reviewed by discussing its potential,
limitations, and prospects.
4.3.1 Pharmaceutical and Pesticide Industry Wastewater
Pharmaceutical compounds are typically detected in urban wastewater at concentrations in the range of nanograms to micrograms per liter [149], with TOC levels in
the low milligrams-per-liter range [150]. Although pharmaceuticals can be resistant
to treatment and have deleterious effects downstream, at the levels they are found in
urban wastewater they do not cause operational problems to the UWTPs. However,
wastewater from pharmaceutical industries presents a distinctive case. These wastewater effluents contain high levels of TOC, with concentrations even reaching grams
per liter [151], and high levels of compounds that are specifically designed to be bioactive and hence have a high potential for toxicity. Because the volumes of water are
much lower than in urban wastewater, Fenton processes are more commonly used
to treat pharmaceutical wastewater, as the high TOC load and lower water volumes
make it feasible to alter the pH to meet the requirements for Fenton processes. However, photocatalysis has also been studied at the lab scale for treatment of pharmaceutical industrial wastewater. Ahmadi et al. used a TiO 2 coupled with carbon nanotubes to treat pharmaceutical wastewater; 0.2 g/L of catalyst was able to reduce the
TOC from 1295 to 228 mg/L in 240 min of irradiation. Deng et al. utilized a silverbased photocatalyst to reduce the TOC of real pharmaceutical wastewater from 25 to
10 g/L in 500 min [152], while Verma et al. used a commercial TiO 2 preparation to
reduce the COD by approximately 90% after 7 h from an initial load of 2.5 g/L.
Industrial wastewater from the pesticide industry is in many ways identical to that
from the pharmaceutical industry. Pesticides, like pharmaceuticals, are bioactive
compounds, are designed to be stable in order to perform their designed function,
and can interfere with biological treatments. HPC has also been studied for the treatment of industrial wastewater from the pesticide industry. Alalm et al. [153] compared the efficiency and cost of using HPC (commercial TiO 2 ) versus a solar photoFenton process for treating real agrochemical/pesticide wastewater with a high
COD load of 7 g/L. The wastewater was treated using parabolic solar collectors and
showed very high efficacy for both processes, especially when taking into account
the COD load present. Under the optimal conditions studied, solar HPC was able
to reduce the COD load by 80%, while the photo-Fenton process reached 91%. As
246
Reprinted from the journal
1 3
4.3 Industrial Wastewater Treatment and Energy Recovery from Hydrogen
Production
Industrial processes utilize water that can be contaminated by any organic or inorganic compounds used in the process. Thus, the characteristics of urban wastewater are completely different from those of industrial wastewater. The role of AOPs
in industrial wastewater treatment is often to improve its biodegradability and/or
reduce toxicity, before applying a biological process. AOPs can also be used after
biological treatment of industrial wastewater to further reduce residual contaminants
to meet the standards for effluent disposal or reuse. In the following subsections, the
application of HPC to various types of industrial wastewater (food, textile, tanning,
and pharmaceutical/pesticide) are critically reviewed by discussing its potential,
limitations, and prospects.
4.3.1 Pharmaceutical and Pesticide Industry Wastewater
Pharmaceutical compounds are typically detected in urban wastewater at concentrations in the range of nanograms to micrograms per liter [149], with TOC levels in
the low milligrams-per-liter range [150]. Although pharmaceuticals can be resistant
to treatment and have deleterious effects downstream, at the levels they are found in
urban wastewater they do not cause operational problems to the UWTPs. However,
wastewater from pharmaceutical industries presents a distinctive case. These wastewater effluents contain high levels of TOC, with concentrations even reaching grams
per liter [151], and high levels of compounds that are specifically designed to be bioactive and hence have a high potential for toxicity. Because the volumes of water are
much lower than in urban wastewater, Fenton processes are more commonly used
to treat pharmaceutical wastewater, as the high TOC load and lower water volumes
make it feasible to alter the pH to meet the requirements for Fenton processes. However, photocatalysis has also been studied at the lab scale for treatment of pharmaceutical industrial wastewater. Ahmadi et al. used a TiO 2 coupled with carbon nanotubes to treat pharmaceutical wastewater; 0.2 g/L of catalyst was able to reduce the
TOC from 1295 to 228 mg/L in 240 min of irradiation. Deng et al. utilized a silverbased photocatalyst to reduce the TOC of real pharmaceutical wastewater from 25 to
10 g/L in 500 min [152], while Verma et al. used a commercial TiO 2 preparation to
reduce the COD by approximately 90% after 7 h from an initial load of 2.5 g/L.
Industrial wastewater from the pesticide industry is in many ways identical to that
from the pharmaceutical industry. Pesticides, like pharmaceuticals, are bioactive
compounds, are designed to be stable in order to perform their designed function,
and can interfere with biological treatments. HPC has also been studied for the treatment of industrial wastewater from the pesticide industry. Alalm et al. [153] compared the efficiency and cost of using HPC (commercial TiO 2 ) versus a solar photoFenton process for treating real agrochemical/pesticide wastewater with a high
COD load of 7 g/L. The wastewater was treated using parabolic solar collectors and
showed very high efficacy for both processes, especially when taking into account
the COD load present. Under the optimal conditions studied, solar HPC was able
to reduce the COD load by 80%, while the photo-Fenton process reached 91%. As
246
Reprinted from the journal