Studies On The Elimination Of Nonylphenol Ethoxylates In The Dyeing Wastewater

Nonylphenol ethoxylates (NPEO) is the focus of the concern of the environment researcher for the weak endocrione effects on the natural water bodies from its biodegradation prouducts, The civil and industry wastewaters are considered to be the sources of the NPEO in the waters. Among the wastewaters, the dyeing wastewater from the denim dyeing industry is famous for its abundant use of NPEO. However little has been known on the fate of NPEO from the wastewaters.With the aid of Major Science and Technology Program for Water Pollution Control and Treatment (2012ZX07206-002), the removal efficiency and eliminating route of NPEO and its by-products in treatment plants are studied. Some biodegradation theories deduced from the urban wastewater treatment plants are confirmed in dyeing wastewater treatment process while the pH is high up 11. Some phenomenons are recorded for the first time. The elimination route of NPEO is proposed based on the facts acquired from the batch and consecutive experiment. Engineering measures are recommended to decrease the endocrine effects originated from the wastewater. The findings mentioned above are summerized below.1. Nonylphenol was determined in the dyeing wastewater from a denim industry park with concentration from 20μg/L to 80 μg/L.80%～98% of NP was removed from the influent in a wastewater treatment plant designed for the conventional pollutants (such as COD, TN and TP) in the denim wastewater, disreagarding the high concentration of alkaline and dyes. The effluent concentration of NP was lowered to 2～20μg/L. The acid sedimentation unit and aerobic biodegradation unit played important role in the eliminating procedure. The increase of NP in the anaerobic hydrolysis unit confirme the production theory of NP from NPEO and showed the nessesities to eliminate NPEO in the wastewater. The adsorption of settling particles to NP is thought to be responsible for the concentration decrease determined in the acid sedimentation unit. But the adsorption theory of aerobic sludge might failed to function for a long hydrolic retention time in the sedimentation units.2. The batch anaerobic experiment reveals that the removal of NPEO is influenced by the alkalinity of the wastewater with a decrease trend. The removal rates of NPEO from wastewaters under the pH 10.2 averaged 54% or so, lower than that in the netural enviroment. Nonylphenol monoethoxylates (NP1EO) and nonylphenol diethoxylates (NP2EO) are the main products among the NPEOs with short chain ethoxy group (EO) in the basic enviroment while NP and NP1EO were found in the neutral environment. With only several hundreds μg/L short-chain NPEO (EO number=1～3, abbrived NP1～3EO below) and NP were detected, most of NPEO eliminated from the waters, amount to 3 thounsands μg/L are suspected to be asorpted by the anaerobic active sludge.3.90% or more NPEO was removed from the wastewaters in 4 hours in the aerobic batch reactor. Most of them are suspected to be transformed nonylphenol polyethoxy carboxylate (NPEC) with long ethoxy group (EO) or be asorpted by the active sludge because only several hundrends μg/L of NP, NP1～3EO and short-chain NPEC (EO number=1～3, abbrived NP1～3EC below) were determined in the outlets.4. The results from the consecutive anaerobic unit are mostly congruous with that from the batch experiment of alkaline environment except for the consentration of NP and NP1～3EO. The concentration determined in the outlet of the consecutive anaerobic unit amouted up to 4-5 mg/L, high up the 500～900 μg/L from the batch experiment. It might be the active sludge adhered to the soft filter with long sludge retention time that results in the surge of NP and NP1～3EO in the consecutive anaerobic unit.5. The elimination rates of NPEO in the consecutive aerobic unit reached up to 81%. NPEO removed are thought to be transformed to NPEC with the same EO number or be mineralized and assimilated by the microorganisms. But the removal rates of NP1-3EO were not as high as that of long-chain NPEO. The residual of total NP1-3EO and NP reached 600～2000μg/L with removal rates around 54～78%. The biodegradation rates of NP1～3EO would be much lower considering their absorption to active sludge.6. The concentration of NP1～3EC are elevated to 2-3.5 and 20～30times high in the contact oxidation and the conventional aerobic active sludge unit respectively. The difference results from the different mixing intensity applied in the aerobic units. More NP1-3EC would be produced when NP1～3EO were blending more thoroughly with active sludge and air like they were treated in the conventional sludge tanks. The contact of sludge with NP1～3EO, occured in the packed contact oxidation units, are more weak that result in the less produce of NP1-3EC.7. Based on the results above, the elimination route of NPEO is proposed below: entering the acid sedimentation unit, NP and NPEO would be absorpted to the bulky particle settling down with the decrease of pH. Then the concentration of NP and NPEO would increase for the transformation of long-chain NPEO in the anaerobic hydrolysis unit. The unit with long sludge retention time will produce more NP and NP1～3EO, which result in the outlet concentration consequently. The removal rate of long-chain NPEO are high up to 91%, partly result from the oxidation occurred in the aerobic unit. NP1～3EO can be removed from the wastewater above 54% on average, parts of them transformed to NP1-3EC. The amounts of NP1-3EC produced are related to the mixing condition in the aerobic unit. A completely mixing of sludge and wasterwater will result in a higher concentration of them. The concentration of NP, NP1～3EO in the outlet of the treatment plant depend on their production in the anaerobic unit and their removal rates in the aerobic unit. The lower sludge retention time of the anaerobic unit will lower the concentration of NP and NPEO and is help for its control. To control the outlet concentration of NP1-3EC, the contact oxidation system is recommended for its higher removal rate of NPEO and lower producing rates of NP1-3EC.NPEC with long-EO-chain is suspected to be one biodegradation product of NPEO. Parts of NPEO are suspected to be absorpted in the sludge settled in the acid-sedimentation unit and anaerobic unit. But for the limitation of detection method of our lab, the distribution of them did not be determined in the study. To fully understand the transformation of NPEO in the dyeing wastewater treatment plants, advanced detection method should be applied and the mass balance should be made in the future.