Sorption of biodegradation end products of nonylphenol polyethoxylates onto activated sludge

Nonylphenol(NP), nonylphenoxy acetic acid(NP1EC), nonylphenol monoethoxy acetic acid(NP2EC), nonylphenol monoethoxylate(NP1EO) and nonylphenol diethoxylate(NP2EO) are biodegradation end products(BEPs) of nonionic surfactant nonylphenolpolyethoxylates (NPnEO). In this research, sorption of these compounds onto model activated sludge was characterized. Sorption equilibrium experiments showed that NP, NP1EO and NP2EO reached equilibrium in about 12 h, while equilibrium of NP1EC and NP2EC were reached earlier, in about 4 h. In sorption isotherm experiments, obtained equilibrium data at 28℃ fitted well to Freundlich sorption model for all investigated compounds. For NP1EC, in addition to Freundlich, equilibrium data also fitted well to Langmuir model. Linear sorption model was also tried, and equilibrium data of all NP, NP1EO, NP2EO and NP2EC except NP1EC fitted well to this model. Calculated Freundlich coefficient(K F) and linear sorption coefficient(K D) showed that sorption capacity of the investigated compounds were in order NP>NP2EO>NP1EO>NP1EC≈NP2EC. For NP, NP1EO and NP2EO, high values of calculated K F and K D indicated an easy uptake of these compounds from aqueous phase onto activated sludge. Whereas, NP1EC and NP2EC with low values of K F and K D absorbed weakly to activated sludge and tended to preferably remain in aqueous phase.

Pollution of NPEOs in four municipal sewage treatment plants in the north of China

The concentration and distribution of nonylphe-nol polyethoxylates(NPEOs represents the mixture,and NPnEO represents the monomer)and its metabolites in the influent and effluent of four municipal sewage treatment plants(STPs)in the north of China were measured.Moreover,the concentration and distribution of the above chemicals in the sludge of two STPs were also determined,and the transfer and fate of NPEOs in the sewage treatment process were discussed primarily by analyzing the distribu-tion of the products in the effluent and the sludge.The results showed that NPEOs and its metabolites existed in all the samples of the influent,effluent,and sludge.NPEOs were degraded in the sewage treatment process with the removal efficiency in the range of 23.38%-77.11%,or an average of 52.86%.However,the large analogs of NPnEO were only degraded to small ones,whose degradation rate was rather slow,and consequently the degradation was not complete.Hence,the concentrations of some small metabolites,such as nonylphenol(NP),nonylphenol monoethoxylate(NP1EO),and nonylphenol diethoxylate(NP2EO)were elevated in the effluent.These small metabolites are more toxic than the large NPnEO analogs,and some of them were reported to exhibit environmental endocrine disrupting activity.From this point of view,the process of sewage treatment does not reduce but elevate the risk of NPEOs,which becomes the main source of these small NPnEO in the environment.The sludge exhibited good adsorption ability for NPEOs,especially for the small analogs,which led to the high level of NPEOs in the sludge.Hence,reasonable disposal of the surplus sludge to avoid re-pollution is very important.