15.2 Photobiological Agents and Methods Used in PhotoBiological Reactors

235

Finally, the applied photo-Fenton configuration also permits micropollutant

degradation, despite the fact that the system’s operational parameters were not

intended for this process. Either in batch or incessant mode, there is a 5-log

bacterial reduction accompanied by a concurrent micropollutant removal (∼33%

in the continuous mode or ∼55% with an extra addition of hydrogen peroxide),

providing a high additional value during this disinfection process. Under normal

working conditions, iron oxides have effectively replaced the use of iron salts, giving

way to an easier and cheaper implementation of the process. Iron oxides have been

proven to be fruitful in maintaining an effective photo-Fenton process. Hence, in

the intended application, there will be no need for acidification of the water and

subsequent neutralization, avoiding costs of acids/bases, generation of salts, and

corrosion of the equipment. Furthermore, easy separation of the catalyst is possible,

as iron oxide particles form residue fairly and quickly. Hence, microfiltration,

magnetic separation (for ferromagnetic oxides), or simple decantation could be suf-

ficient. Efficiency wise, the 5-log reduction of fecal bacteria enables safe discharge

and efficient reuse, with balancing removal of emerging contaminants. Overall, the

results of this work prove that channel pond reactors are indeed a solution with

a potential for disinfection and decontamination by the photo-Fenton process at

near-neutral pH, given the appropriate residence time, land use, and wastewater

quantities [19].

15.2.2.3

Photochemical Approaches in the Treatment of Wastewater

Flow Reactor: (Chemical [Photo-Activated] Treatment) Recent study presents the inte-

grated degradation of p-NTS (p-nitro toluene-o-sulfonic acid) by combining

photochemical (Fenton) and biological flow reactors. The degradation of p-NTS

is not possible by wastewater bacteria, and it is considered as a nonbiodegradable

intermediate during the manufacture of dyes, surfactants, and brighteners.

A concomitant 20–25% decrease in the initial carbon content during the photo-

chemical pretreatment was observed along with the abatement of the aromaticity.

This study shows that the intermediates produced in the pretreatment stage are

biodegradable. After pretreatment, a minimum residual (<0.2 mg/l) was attained,

and this level of oxidant did not interfere with the subsequent biological degradation.

The influence of the reaction parameters such as input concentration of p-NTS, rate

of hydrogen, O2 addition, reactor flow rate, TOC reduction rate, and BOD/COD as

a function of the time of chemical pretreatment is reported. At flow rates of 0.18 l/h

(∼5.5 hours residence time), a photochemical degradation efficiency of 75%, a bio-

logical degradation efficiency of 52%, and an overall degradation efficiency of 88%

for the coupled process were observed. The disappearance of pNTS in the photo-

chemical reactor, the growth and degradation of the benzoquinone such as aromatic

intermediate, and production of short-chain aliphatic compounds are reported as a

function of pretreatment time. The increase in BOD/TOC as a function of pretreat-

ment time has been correlated to the p-NTS and aliphatic recalcitrants existing in

the solution.

The biological degradation was observed to be strongly dependent on the flow rate

and pollutant load of the solution. These were the two main parameters affecting