Treatment of industrial wastewater using photooxidation and bioaugmentation technology.

The versatile metabolism of microorganisms has an played important role in the biodegradation of recalcitrant toxic compounds entering into the natural environment. The biodegradability of organics can be enhanced using bioaugmentation and advanced oxidation processes (AOP) for aerobic/anaerobic treatment programs. Wastewater from a bulk drug (cresol) plant had high levels of TDS, COD and BOD, whilst the levels from a pigment plant low. Both contained organics difficult to degrade. AOP using hydroxyl radical generated in 1 L glass reactor using UV and H2O2 efficiently oxidised phenol and cresol. COD and sulphite reduction in cresol containing wastewater were 20-60% in 1-6 h. A twenty to thirty percent reduction in copper phthalocyanine pigment effluents was achieved in 6 h using AOP. Strains of Micrococcus, Pseudomonas, and Nocardia degrading phenol, cresol were isolated from soil and sludge. Mixed biomass of these organisms removed phenols (1,000 ppm) and cresols (500 ppm) completely in 24 and 72 h, respectively. The COD and BOD reductions under the optimum nutritional and physiological conditions were in the range of 70 to 90%. When added to the bioreactor, 20% of the developed biomass of mixed strains of Micrococcus, Nocardia and Pseudomonas increased the rate of COD and BOD reduction gradually and stabilised at 80-90%. Added biomass improved the overall efficiency of the aerobic process.     

Performance of high-rate sludge digesters fed with sonicated sludge.

A major limitation of anaerobic sludge digestion is the long hydraulic retention time (HRT) required for satisfactory stabilization which results in large digester size. This study explored a possibility of operating digesters at shortened HRTs by sonication pretreatment of secondary sludges. Four identical digesters designated D1, D2, D3 and D4 were fed with untreated and sludge sonicated at densities of 0.18 W/ml, 0.33 W/ml and 0.52 W/ml, respectively. All digesters were operated at three HRTs of 8-day, 4-day and 2-day. Comparing with the control digester (D1), total solids removal efficiencies improved by 12-19%, 17-36% and 20-39% in digesters D2, D3 and D4, respectively. The volatile solids removal was also increased by 11-21%, 17-33% and 19-36% in the respective digesters. The improved solids degradation corresponded with increase in biogas production by 1.4-2.5, 1.9-3.0 and 1.6-3.1 times, respectively. Increase in methane composition by 2-17% was also noted in all digesters fed with sonicated sludge. An analysis indicated that sonication pretreatment could enhance degradation of carbon, nitrogen and sulfur substances in the digestion. The study suggested that sonication of sludge is a possible pretreatment to shorten the digester operating HRT with improvement in solids degradation, biogas production and methane content. It can be deduced that to maintain a consistent solids loading at a desire performance, sludge digester with smaller size can be designed.     

Aerobic biological treatment of thermophilically digested sludge

Aerobic biological treatment of digested sludge was studied in a continuously operated laboratory set-up. An aerated reactor was filled with thermophilically digested sludge from the Moscow wastewater treatment plant and inoculated with special activated sludge. It was then operated at the chemostat mode at different flow rates. Processes of nitrification and denitrification, as well as dephosphatation, occurred simultaneously during biological aerobic treatment of thermophilically digested sludge. Under optimal conditions, organic matter degradation was 9.6%, the concentrations of ammonium nitrogen and phosphate decreased by 89 and 83%, respectively, while COD decreased by 12%. Dewaterability of digested sludge improved significantly. The processes were found to depend on hydraulic retention time, oxygen regime, and temperature. The optimal conditions were as follows: hydraulic retention time 3-4 days, temperature 30-35 degrees C, dissolved oxygen levels 0.2-0.5 mg/L at continuous aeration or 0.7-1 mg/L at intermittent aeration. Based on these findings, we propose a new combined technology of wastewater sludge treatment. The technology combines two stages: anaerobic digestion followed by aerobic biological treatment of digested sludge. The proposed technology makes it possible to degrade the sludge with conversion of approximately 45% volatile suspended solids to biogas, to improve nitrogen and phosphorus removal in reject water from sludge treatment units, and to achieve removal of malodorous substances after 8-9 days of anaerobic-aerobic sludge treatment.     

Characterization of sludges for predicting anaerobic digester performance.

Batch anaerobic digestion tests of primary sludge and waste activated sludge were conducted for a duration of 123 days to determine the ultimate degradability of the sludges. For primary sludges the inert fraction of the particulate COD that was predicted by the wastewater models could be employed to predict their biodegradability under anaerobic conditions. The degradation of waste activated sludge was adequately characterized for the first 60 days of digestion using a model that assumed equivalent biodegradability of particulate COD components under aerobic and anaerobic conditions. However after 60 days of anaerobic digestion it appeared that decay of the endogenous products was occurring. This could be described with a first order decay function with a coefficient of 0.0075 d(-1). For continuous flow digesters operating at SRTs of 30-60 days, the predicted VSS destruction with the modified model was approximately 10% higher than that predicted on the basis of inert endogenous decay products.     

A pilot study on accelerated sludge degradation by a high-concentration membrane bioreactor coupled with sludge pretreatment.

A new sludge treatment process combining a high MLSS membrane bioreactor with sludge pretreatment techniques was studied in pilot-scale experiments. The membrane bioreactor (MBR) was adopted for high efficiency aerobic digestion. The combination of alkaline-ozone treatment of the mixed liquor in the MBR reactor accelerated the biodegradation process by enhancing biodegradability of the sludge. The hydraulic retention time (HRT) of the reactor was set as 3.1 days and the DO level was 1 mg/L on average. After 5 months of operation, the accumulative total solids reduction was more than 70%. Removal efficiency of volatile solids and non-volatile solids were 76% and 54%, respectively. It was found that a considerable portion of the non-volatile solids was dissolved into ions and then flushed out with the effluent. Also, about 41% and 28% of T-N and T-P in the raw sludge were removed although no biological nutrient removal process was adopted. The experiment was run smoothly without significant membrane fouling, even at the relatively high levels of MLSS concentration (11,000-25,000 mg/L). It is concluded that the newly proposed process can significantly increase the sludge reduction efficiency with much shorter retention times.     

Is sonication effective to improve biogas production and solids reduction in excess sludge digestion?

Results of three semi-continuous anaerobic tests were reported and discussed. Each test was carried out by two parallel anaerobic reactors fed with waste activated sludge, either as it was sampled from the sewage treatment plant of Rome North or previously disintegrated by ultra-sound treatment. Activated sludge was sonicated at the energy input of 5,000 or 2,500 kJ kg(-1) dry solids corresponding to a disintegration degree of approximately 8 or 4%, respectively. Sonication proved to be effective both in increasing VS destruction and cumulative biogas production. The best increase of VS destruction (from 30 to 35%) was achieved in test #3 carried out at high organic load (10 d residence time) and low energy input (2,500 kJ kg(-1) dry solids). The best increase in cumulative biogas production (from 472 to 640 NL after 67 d of tests i.e.) was obtained in test #1 at low organic load (20 d residence time) and high energy input (5,000 kJ kg(-1) dry solids). Specific biogas production varied in the tests carried out with untreated sludge (0.55 - 0.67 Nm3 kg(-1) VS destroyed) but was practically unchanged for all the tests with sonicated sludge (0.7 Nm3 kg(-1) VS destroyed).     

Anaerobic biodegradation of estrogens--hard to digest.

Although many publications are available on the fate of estrone (E1), 17beta-estradiol (E2) and 17alpha-ethynylestradiol (EE2) during aerobic wastewater treatment, little is published on their fate under strictly anaerobic conditions. Present research investigated the digestibility of E1 and EE2, using digested pig manure, granular UASB sludge, UASB-septic tank sludge and activated sludge as inocula. Besides, actual concentrations were measured in a UASB septic tank treating black water. Under anaerobic conditions E1 is reduced to E2 but the extent of this reduction depends on type of inoculum. No significant loss of the sum of E1 and E2 and of EE2 was observed. Adsorption was responsible for a 32-35% loss of E1 and E2 from the liquid phase in the UASB septic tank and the effluent still contained considerable concentrations of respectively 4.02 microg/l and 18.79 microg/l for E1 and E2 with a large fraction present in conjugated form. No EE2 was detected in the UASB effluent.     

Advanced treatment by anaerobic process followed by aerobic membrane bioreactor for effluent reuse in paper mill industry.

The operation of an activated sludge process at a paper mill (AIPM) in Hedera, Israel, was often characterized by disturbances. As part of a research and development project, a study on new biological treatment was initiated. The study included the operation of three pilot units: a. anaerobic treatment by upflow anaerobic sludge blanket (UASB); b. aerobic treatment by two pilot units including activated sludge and membrane bioreactor (MBR), which have been operated in parallel for comparison reasons. The pilot plant working on anaerobic treatment performed COD reduction from 2,365 to 755 mg/L, expressed as average values. Based on the pilot study, a full scale anaerobic treatment system has been erected. During a period of 100 days, after achieving steady state, the MBR system provided steady operation performance, while the activated sludge produced effluent characterized by oscillatory qualities. The following results, based on average values, indicate much lower suspended solids concentrations in the MBR effluent, 2.5 mg/L, as compared to 25 mg/L in the activated sludge. The ability to develop and maintain a concentration of over 11,000 mg/L of mixed liquor volatile suspended solids in the MBR enabled an intensive bioprocess at relatively high cell residence time. This study demonstrates that the anaerobic process, followed by aerobic MBR can provide effluent of high quality which can be considered for economic reuse in the paper mill industry.     

ABR反应器对垃圾渗滤液的处理试验研究

ABR工艺在处理垃圾渗滤液中具有其他厌氧生物反应器所达不到的优点。尤其是对B/C低、氨氮浓度高、COD浓度高的废水处理,通过调节回流比、HRT、碱度等参数后,可以取得很好的处理效果。在本次实验中,HRT控制在18h后明显提高的垃圾渗滤液的可生化性及C/N,使ABR出水CODcr去除率达到75%,C/N为6.72,对后续好氧反应起到了重要作用。在调控一定回流比后,为提供厌氧氨氧化所需的电子受体NO-3和NO-2实现脱氮。反应器在经过120d的培养驯化,氨氮进水为460mg/L,ABR对氨氮的去除率稳定在80%。不同格室的厌氧颗粒污泥都得到很好的驯化并在其合适的环境中发挥各自的功能。     

Automated equipment for anaerobic sludge parameters determination.

Methanogenic activity, anaerobic biodegradability and toxicity are key parameters in the design and operation of anaerobic bioreactors. A large variety of methods exist for the determination of these parameters but a normalized method has not been established so far. This paper presents the development of an automated manometric system for the determination of these anaerobic sludge parameters. The system is based on monitoring the production of methane by using a pressure transducer that measures the pressure in a gas-collecting chamber of known adjustable volume, which is independent of the space where biogas production takes place. The evolution of pressure generated by the accumulation of methane relates to the conversion of COD. In this way, the methanogenic activity of the sludge can be determined, as well as the biodegradability of solids and liquid, as well as the methanogenic toxicity of compounds. The equipment permits gas sampling, as well as extraction and introduction of liquid, without losing the anaerobic conditions. Various assays have been conducted to test the reliability and reproducibility of the obtained results, showing a high level of both. The methanogenic activities obtained in the assays ranged between 0.1 and 1.8 g COD g(-1) VSS d(-1), and the biodegradability of the organic compounds tested ranged between 20 and 90%.     

A comparison of ultrasound treatment on primary and secondary sludges.

Ultrasound treatment of primary and secondary sludges was conducted to improve the qualities of sludges for the anaerobic digestion. The impacts of different sonication times, sonication densities and solids concentrations on ultrasonication efficiency were examined. The experimental results indicated that the significant reduction in particle size and increase in soluble organics could be achieved, implying that ultrasonication could offer a feasible treatment method to efficiently disintegrate sludge. The greater decrease in particle size and increase in soluble organics of sludge indicated that the secondary sludge has a more remarkable improvement after sonication over the primary sludge. With respects to the extent of disintegration and energy consumption, higher sonication density performed more effectively in terms of specific energy. There exists an optimal solids concentration range for both the sludges for optimum sonication. Within the optimal solids concentration range, efficient sonication can be effected and sludge would be disintegrated efficiently. The ultrasound would be attenuated by scattering and absorption if the solids concentration exceeds the optimal range. It appeared from the study that the mechanical shear forces caused by ultrasonic cavitation could be a key factor for sludge disintegration and collapse of cavitation bubbles could significantly alter the sludge characteristics.     

Biological nutrient removal in simple dual sludge system with an UMBR (upflow multi-layer bioreactor) and aerobic biofilm reactor.

In this study, a simple dual sludge process was developed for small sewage treatment. It is a hybrid system that consists of upflow multi-layer bioreactor (UMBR) as anaerobic and anoxic reactor with suspended growth microorganisms and post aerobic biofilm reactor with inclined plates. UMBR is a multifunction reactor that acts as primary sedimentation tank, anaerobic reactor, anoxic reactor, and thickener. The sludge blanket in the UMBR is maintained at a constant level by automatic control so that clear water (30 mg-SS/L) can flow into the post aerobic biofilm reactor. It leads to improving performance of the biofilm reactor due to preventing of excess microbial attachment on the media surface and no requirment for a large clarifier caused by low solid loading. The HRT in the UMBR and the aerobic biofilm reactor were about 5.8 h and 6.4 h, respectively. The temperature in the reactor during this study varied from 12.5 degrees C to 28.3 degrees C. The results obtained from this study show that effluent concentrations of TCOD, TBOD, SS, TN, and TP were 29.7 mg/L, 6.0 mg/L, 10.3 mg/L, 12.0 mg/L, and 1.8 mg/L, which corresponded to a removal efficiency of 92.7%, 96.4%, 96.4%, 74.9%, and 76.5%, respectively. The sludge biomass index (SBI) of the excess sludge in the UMBR was about 0.55, which means that the sludge in the UMBR was sufficiently stabilized and may not require further treatment prior to disposal.     

Analysis of phosphorus removal and anaerobic selector performance in a full-scale activated sludge process in Singapore.

This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed.     

Anaerobic reactor/high rate pond combined technology for sewage treatment in the Mediterranean area.

Two high-rate, anaerobic/aerobic units were used to treat the sewage of the Institut Agronomique st Vétérinaire Hassan II (Morocco) campus in a 1,100 m2-plant designed for 1,500 e.p. and receiving 63 m3 per day. The anaerobic pre-treatment consisted of a two-step up-flow anaerobic reactor (TSUAR) comprising two reactors and one external settler all in series. The aerobic line, or post-treatment, consisted of a high-rate algal pond (HRAP) and one maturation pond in series. The system totalized a hydraulic retention time (HRT) of 9 days. A gravel filter (GF) was constructed behind the TSUAR to trap low-density particles. The TSUAR removed 80% of COD and 90% of SS within 48 h. Solids retention time in the reactors averaged 32 d with a specific sludge production of 0.28 g SS g(-1) COD removed. Almost 93% of the sludge evacuated from the settler was stabilized. Specific biogas production from both reactors was 0.25m3 kg(-1) COD removed. Used in this configuration, the HRAP lost its BOD removal activity and increased its nutrients and pathogens removal capabilities (tertiary treatment). Results showed that 85% of total nitrogen and 48% of total phosphorus were removed by the HRAP. Land area requirement of this combination was less than 1 m2 per capita and filtered final effluent was of excellent quality (COD, 82 mg/l; TKN, 8.3 mg/l; total P, 2.7 mg/l, faecal coliforms, 2.4 10(3)/100 ml and zero helminths eggs).     

Adsorption and biodegradation of azo dye in biofilm processes.

The removal of a common azo dye, acid orange 7 (AO7), in biofilm systems was investigated in this study. The abiotic and biotic fate of AO7 was examined under a variety of operating conditions: aerobic nitrification, anoxic denitrification and anaerobic digestion. A comparison of the performance between biofilm and activated sludge treatment processes was made. The adsorption of AO7 onto biofilm matrix and activated sludge flocs was found to fit the Langmuir equation. However, there is a significant difference in the adsorption capacities between biofilm and activated sludge. AO7 was recalcitrant in both biofilm and activated sludge systems under aerobic conditions. Under anaerobic conditions, AO7 was readily decolorized. AO7 decolorization was also observed under anoxic conditions. However, the presence of nitrate inhibited AO7 decolorization.     

Potentially toxic element release by fenton oxidation of sewage sludge.

The presence, in sewage sludge, of excess levels of the potentially toxic elements (PTE) copper, zinc, chromium, cadmium, nickel, lead and mercury, could impact on our ability to recycle these residues in the future. Far stricter limits on the levels of PTEs are likely in proposed legislation. A method involving the dosing of Fenton's reagent, a mixture of ferrous iron and hydrogen peroxide, under acidic conditions was evaluated for its potential to reduce metal levels. The [Fe]:[H2O2] (w/w) ratio was found to give a good indication of the percentage copper and zinc elution obtainable. Sites with no iron dosing as part of wastewater treatment required extra iron to be added in order to initiate the Fenton's reaction. A significant reduction, in excess of 70%, of the copper and zinc was eluted from both raw primary and activated sludge solid fractions. Cadmium and nickel could be reduced to below detection limits but elution of mercury, lead and chromium was less than 40%. The iron catalyst concentration was found to be a crucial parameter. This process has the potential to reduce the heavy metal content of the sludge and allow the recycling of sludge to continue in a sustainable manner.     

Winery and distillery wastewater treatment by anaerobic digestion.

Anaerobic digestion is widely used for wastewater treatment, especially in the food industries. Generally after the anaerobic treatment there is an aerobic post-treatment in order to return the treated water to nature. Several technologies are applied for winery wastewater treatment. They are using free cells or flocs (anaerobic contact digesters, anaerobic sequencing batch reactors and anaerobic lagoons), anaerobic granules (Upflow Anaerobic Sludge Blanket--UASB), or biofilms on fixed support (anaerobic filter) or on mobile support as with the fluidised bed. Some technologies include two strategies, e.g. a sludge bed with anaerobic filter as in the hybrid digester. With winery wastewaters (as for vinasses from distilleries) the removal yield for anaerobic digestion is very high, up to 90-95% COD removal. The organic loads are between 5 and 15 kgCOD/m3 of digester/day. The biogas production is between 400 and 600 L per kg COD removed with 60 to 70% methane content. For anaerobic and aerobic post-treatment of vinasses in the Cognac region, REVICO company has 99.7% COD removal and the cost is 0.52 Euro/m3 of vinasses.     

Development of an ecologically sustainable wastewater treatment system

The present study aimed mainly for the development of a wastewater treatment system incorporating enhanced primary treatment, anaerobic digestion of coagulated organics, biofilm aerobic process for the removal of soluble organics and disinfection of treated water. An attempt was also made to study the reuse potential of treated water for irrigation and use of digested sludge as soil conditioner by growing marigold plants. Ferric chloride dose of 30 mg/l was found to be the optimum dose for enhanced primary treatment with removals of COD and BOD to the extent of 60% and 77%, respectively. Efficient anaerobic digestion of ferric coagulated sludge was performed at 7 days hydraulic retention time (HRT). Upflow aerobic fixed film reactor (UAFFR) was very efficient in removals of COD/BOD in the organic loading rate (OLR) range of 0.25 to 3 kg COD/m(3)/day with COD and BOD removals in the range 65-90 and 82-96, respectively. Photo-oxidation followed by disinfection saved 50% of chlorine dose required for disinfection of treated effluent and treated water was found to be suitable for irrigation. The result also indicated that anaerobically digested sludge may be an excellent soil conditioner. From the results of this study, it is possible to conclude that the developed wastewater treatment system is an attractive ecologically sustainable alternative for sewage treatment from institutional/industrial/residential campuses.     

Characterization, management and treatment of wastewater from white wine production.

During a 16 months period, the characteristics of the wastewaters generated in a Rias Baixas winery (Spain) producing white wine were determined: The characterization study showed that white wine wastewater had an average CODt and TSS values of 7.3 and 5.2 kg/m3, respectively being the ratio wastewater/wine produced of about 1.6-2.0 L/L and the ratio between load pollution and produced wine of 9.7 kg(CODt)/m3(WINE). A strategy for the management of wastes and wastewaters allowed for an important reduction of a 55% of wastewater generation to be achieved. In order to select a suitable technology for the treatment of wastewaters two configurations were tested at pilot scale: i) An Anaerobic Filter (AF) of 430 L followed by an activated sludge unit of 510 L and: ii) one activated sludge unit of 510 L. The results showed that the anaerobic/aerobic configuration was more flexible as it adapted quickly to the different loads and flows produced during the different phases through the year. Besides it allowed higher COD removals (98.5-99.2%) to be achieved and proved to permit a quicker re-start up after starvation periods.     

Treatment of organic synthesis wastewater using anaerobic packed bed and aerobic suspended growth bioreactors.

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg x m(-3) x d(-1). The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg x m(-3)x d(-1) and the aerobic reactor with 0.33 kg x kg(-1) x d(-1), being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%.