Acidogenic-aerobic treatment of industrial estate mixed wastewater | |
| Author | Hossain, Md. Delwar |
| Call Number | AIT Diss. no. EV-98-2 |
| Subject(s) | Factory and trade waste Industrial districts |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Suspended and particulate matter comprise a significant amount of the organic loads in most wastewater. Such suspended and particulate organic matter are not readily biodegradable and need to be solubilized, either aerobically or anaerobically, at some stage in the treatment process to a form suitable to be transported into the microbial cells before they get degraded. This study attempted to incorporate an up-flow anaerobic hydrolysis/acidogenesis reactor (HAR) for the solubilization of suspended and particulate organics of wastewater, and to investigate its effect on removal efficiency, stability and sludge/biofilm characteristics in the completely mixed, cascade and attached growth aerobic activated sludge processes. This was accomplished through on-site pilot scale experiments (phase-I) using industrial estate mixed wastewater and laboratory scale experiments using synthetic wastewater as well as industrial estate mixed wastewater (phase II). The study commenced with an extensive sampling and analysis program, in order to characterize the industrial estate mixed wastewater at three selected industrial estates in Thailand. Results of the sampling and analysis revealed that about 50% of the organic matter (as COD) in each of the industrial estates exits in suspended and particulate form, while 60 to 80% of the nitrogen was found to be in organic forms. Concentration of the heavy metals in the mixed wastewater was found to be consistently low in each of the industrial estates. Treatability studies showed that the aerobic biodegradability of such wastewater could be improved by 30-35% through an anaerobic acid phase pretreatment. The upflow HAR studied in this research, fed with the total wastewater flow, effectively carried out suspended and particulate matters retention, solubilization/acidification and clarification in a single reactor. The operating conditions of the HAR were found to be a strong function of the types and characteristics of wastewater. Under the experimental conditions, considering the efficiency of suspended solids retention, solubilization, acidification and ammonification, the optimum hydraulic retention time (HRT) was between 3-4 hr with the resulting organic loading between 7.20 to 6.40 kgCOD/(m3 .d) in the HAR for various wastewater. Attempts were made to optimize the solubilization and acidification of organics in the total wastewater flow rather than removal of organics at this stage as methane; so that the resulting easily degradable fermentation products (soluble organics- volatile fatty acids, ammonium nitrogen, etc.) could either be removed at higher rates in the subsequent aerobic stage or they could be used as a non-conventional sources of readily degradable organic carbon for enhanced biological nutrient removal in the integrated acidogenic-aerobic systems. Under the conditions investigated in the pilot scale and the laboratory scale experiments, the observed rates ofbiodegradation and the corresponding removal efficiencies of COD, TKN and P in the aerobic processes with the HAR (i.e. acidogenic-aerobic processes) were 8-12%, 15-20% and 10-20%, respectively, higher compared to the ones in the aerobic processes alone. It was found that the higher the fraction of suspended and particulate organics in wastewater, the more significant was the effect of incorporation of the HAR with aerobic processes with respect to the removal efficiencies. Incorporation of the HAR reduced the variability of the readily - 111 -I biodegradable soluble organics in the influent wastewater and thus improved the overall stability of the integrated acidogenic-aerobic processes. Analysis of the sludge/biofilm growth and characteristics revealed that incorporation of the HAR resulted in about 8 to 10% decrease in the overall sludge yield, while the settleability and the dewaterability of the sludge were significantly improved. Bio film analysis showed that the biomass which developed in the attached growth systems with the HAR was more compact and thin; the average density being 10 to 15% higher and with a larger fraction of the active biomass compared to systems without the HAR. Further investigations showed that during the periods of recirculation of activated sludge (RAS) into the HAR, denitrification and phosphate release proceeded well utilizing the volatile fatty acids originating from the hydrolysis of suspended and particulate organics in the HAR. This resulted in significant improvement of the total nitrogen (30-35%) and phosphorus (25-30%) removal efficiencies in the integrated acidogenic-aerobic systems. It was observed that the removal efficiencies of total nitrogen and phosphorus increased with the increase in RAS rates into the HAR. This implies that the solubilized organics in the HAR can serve as an effective source of non-conventional organic carbon for biological nutrient removal from wastewater. It was found that denitrification and phosphate release, using the solubilized organics in the HAR as the source of carbon, progressed at comparable rates with the synthetic chemical (Na.AC) used as the source of organic carbon. The observed rates were 4.98 and 5.87 mgCOD/(mg N03-N) removed when the acetate and the effluent of the HAR were used as the source of organic carbon, respectively; while for the phosphorus release the corresponding rates were 1.43 and 1.64 mgP04-P/gMLSS.h, respectively, for the industrial estate mixed wastewater. Capital investment and operation and maintenance costs for the design flow rate of 15000 m 3 /d were estimated for the attached growth activated sludge process (AGASP) with and without the HAR. It was found that to achieve a similar degree of organic removal, the total investment cost and the operation and maintenance cost of the AG ASP system with the HAR would be lower by about 6.5% and 12.5%, respectively, compared to the same without the HAR. For a repayment period of 20 year, the annualized overall cost of treatment including sludge disposal was found to be 2,140 and 2,360 Baht/m 3 of wastewater for the AGASP with and without the HAR, respectively. |
| Year | 1998 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Eckhardt, Ing. Heinz; |
| Examination Committee(s) | Chongrak Polprasert ;Annachhatre, Ajit P. ;Bechter, Clemens ;Stoll, Ing. Uwe ;Orth, Hermann |
| Scholarship Donor(s) | Deutsche Gesellschaft fuer Technische Zusammenarbeit (GTZ) ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1998 |