Anoxic–oxic activated‐sludge of cyanides and phenols

Abstract

The anoxic-oxic activated-sludge process has been evaluated in a laboratory investigation as a means for effective treatment of cyanide-laden wastewaters, with phenols used as the organic carbon sources for denitrification reactions. The performance of the process was evaluated at different levels of feed cyanide concentration and mean cell residence time (MCRT). The results obtained indicate that the phenolic compounds used can be effectively used as the organic carbon sources to promote denitrification reactions. The effects of cyanide inhibition on overall TOC removal can be alleviated at longer MCRTs. Between 1.2 and 2.2 g TOC can be utilized per gram NO(2) + NO(3) (-) -N removed in the anoxic chamber depending on the prevailing MCRT. Microbial oxidation of cyanide and thiocyanate which yields ammonia is the main mechanism responsible for the removal of cyanide and thiocyanate observed in the anoxic-oxic activated-sludge process. Excellent removal efficiencies have been observed with feed concentrations up to 60 mg CN(-)/L and 100 mg SCN(-)/L Frequent exposure of autotrophic and aerobic cyanideutilizing microbes does not impede their activities in the oxic environment. Good nitrification and denitrification efficiencies are attainable in the anoxic-oxic activated-sludge process in the presence of high feed cyanide and thiocyanate concentrations, provided that MCRT is maintained at a desirable level. As a result, the microbial degradation of cyanide and thiocyanate in conjunction with nitrification and denitrification to produce innocuous nitrogen gas is feasible in the anoxic-oxic activated-sludge process.

Simultaneous removal of phenol, ammonium and thiocyanate from coke wastewater by aerobic biodegradation

“…6, the concentration of NH 4 + -N in the effluent is usually greater than that of the influent. This is due to the presence of organic nitrogen and thiocyanate in the influent, since the former is transformed into NH 4 + during the process of biodegradation and the latter into NH 4 + , CO 2 and SO 4 2− [16,17,20]. This behaviour was confirmed by means of respirometric assays employing synthetic water containing SCN − and not NH 4 + ; it being observed that the biodegradation of the thiocyanate gave rise to the generation of ammonia.…”

“…The experimental data were fitted to an exponential curve (r = 0.982) which suggests that from 75 h on no higher removal than 65.6% would be achieved, even by increasing the HRT. Nitrification does not take place using HRT below 12 over SCN − biodegradation, resulting in low removal efficiency [16][17][18]. In this case, the concentration of NH 4 + -N in the influent was both very high and variable (ranging from 506 to 1108 mg/L) due to certain problems in the prior stripping treatment carried out at the steelworks.…”

Inhibitory effects of toxic compounds on nitrification process for cokes wastewater treatment

“…Fortunately, free cyanide below 0.1 mg/L flowed into nitrification process of full-scale cokes wastewater treatment facility owing to its anaerobic degradation under denitrification condition (Table 1). According to a report of Richards and Shieh [24], free cyanide can be removed to some degree by anaerobic bacteria. Therefore, there was less possibility of incomplete nitrification by toxic effect of free cyanide under normal condition, but an abnormal influx of free cyanide into nitrification process may cause an irrecoverable damage to nitrifying bacteria.…”

On-line estimation of key process variables based on kernel partial least squares in an industrial cokes wastewater treatment plant

“…The wastewater consists of ammonia, cyanide, thiocyanate, sulfides, and a wide variety of complex hydrocarbons such as phenolics, polynuclear aromatic hydrocarbons, and various heterocyclic compounds [3,4]. Most of the chemical oxygen demand (COD) originates from phenol, which is a toxic inhibitory substrate but is also a useful carbon source for acclimatized microorganisms [5]. Cyanide is a highly toxic organic compound even at low concentrations and its presence in aqueous media is severely restricted by regulations [6,7].…”