Coking wastewater is a typical toxic organic wastewater which are difficult to
dispose; it accounts for one of the largest discharges of industrial wastewater in China.
The high concentrations of phenols, cyanide and ammonia cause many problems in
biological treatment which can be solved by pretreatment. In this study, we screened
high feasibility of advanced oxidation processes for coking wastewater pretreatment.
Under the concept of " treat waste with waste ", the advanced oxidation methods were
screened and the manganese ore tailings in pretreatment process was investigated.
This study is based on actual coking wastewater. First screen and combine
advanced oxidation pretreatment process by experiment, including Fenton, analogous
Fenton, ozone, manganese ore tailings catalytic. Then optimize the selected
pretreatment process and study the characterized pollutant removal and transformation
mechanisms including phenol and phenylamine by water and solid analysis. Finally
study the biodegradability and toxicity of pretreatment process effluent and evaluate the
pretreatment process and supply reasonable pretreatment processes. The results show
that:
(1) The UV254 can reflect biodegradability of coking wastewater. In this study ,the
equation of UV254 and B/C is y = 0.4347x-1.905, R2 = 0.9928.
(2) In low concentrations of coking wastewater pretreatment process, manganese
ore tailings can replace divalent iron of Fenton reagent. The COD removal rate can
reach 55.4% and B/C value can reach 0.43 when the dosage of manganese ore tailings is
15g/L and the hydrogen peroxide is 2g/L at room temperature.
(3) The best combination pretreatment of high concentrations of coking wastewater
is using manganese ore tail + ozone after Fenton reagent. The COD removal rate can
reach 53.3% and B/C value can reach 0.539, when the hydrogen peroxide: divalent iron
is 10: 1, the hydrogen peroxide dosage 7g/L reaction time is 30min, the manganese ore
tailings dosage is 1g/L and the ozone access time is 30min at room temperature.
(4) Phenol and phenylamine removal rate can reach 88.3% and 71.0% in high
concentrations of coking wastewater after pretreatment, and are all transformed to
quinone as intermediate. The manganese ore tailings have a preference for phenylamine
removal characteristic,when phenol and phenylamine exist at the same time.The
manganese ore tailings have catalytic oxidation rather than adsorption in the
pretreatment process as the major mechanism to remove COD.
(5) The activated sludge dehydrogenase inactivation rate reduced from 93% to
36.8% after the pretreatment of coking wastewater.
(6) Recommendation of the pretreatment process: low concentrations of coking
wastewater flows past a packed column of manganese ore tailings after adding hydrogen
peroxide; high concentrations of coking wastewater flows past a packed column of
manganese ore tailings after treated by Fenton reagent and ozone at the bottom the same
time.
Key Word: coking wastewater, pretreatment process, manganese ore
tailing, advanced oxidation process, phenol, phenylamine