Modeling of anaerobic treatment of wastewater in ponds | |
| Author | Rajbhandari, Binod Kumar |
| Call Number | AIT Diss. no.EV-04-02 |
| Subject(s) | Sewage--Purification Ponds--Sanitation |
| 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 |
| Series Statement | Dissertation ; no. EV-04-02 |
| Abstract | Anaerobic ponds (APs) are popularly employed for treatment of organic wastewater emanating from variety of industries such as food, pulp and paper, sugar and distillery. Anaerobic ponds are pa1ticularly effective in treating high-strength wastewaters containing biodegradable solids as they achieve the dual purpose of sedimentation of particulate matter and anaerobic conversion of organics. Accordingly, this research aims at assessing the performance of APs under various operating conditions such as feed organic loading rates and COD: S04 ratios. Since APs serves as a bioreactor for organic matter conversion, the relative conversion of organic matter in anaerobic pond sediment as well as in bulk liquid layer are assessed. Furthermore, mathematical model are also developed to describe the anaerobic pond performance. This research on anaerobic; treatment of wastewater in ponds is conducted in three phases. i) Full scale investigation ii) laboratory scale investigation and iii) Modeling Full-scale investigation: Investigations on the existing full-scale wastewater anaerobic pond system were carried out in a tapioca starch and glucose factory situated in the Central province of Thailand with a capacity of 250 tons starch/day. The factory uses groundwater as a source for process water, and generates combined wastewater of approximately 5,000 m3/d. The operating ambient temperature during the period of investigation was in the range of 30-35°C. The wastewater treatment system consists of 21 anaerobic ponds (APs) and facultative ponds (FPs) connected in series with total area of about 36.5 hectares. Out of these, 6 are AP with area of 7.39 hectares and 15 are FP with 29.11 hectares .. The average pollution load was calculated to be 63,258 kg COD/d. The overall removal rate for COD, BOD5, TSS and OS were 96.2 %, 98.2%, 94. 7% and 71.4%, respectively. However, the quality of treated effluent from the series of anaerobic ponds still did not meet the effluent standard, therefore, fu1ther treatment of treated wastewater from the anaerobic pond system is required. Laboratory scale investigation: Lab-scale investigations were conducted to study the effect of organic loading rates as well as COD and sulfate ratio on anaerobic pond performance. Two column in series anaerobic pond and four rectangular anaerobic ponds were operated with various combination of organic loading rates from 150 to 600 g COD/m3d and COD: S04 ratio from 5 to 20. The result depicted that, the organic removal performance increased considerably by increasing organic loading rates from 150 to 600 g COD/m3d. The result from experiment on column in series reactor revealed that, HRT of 3 days could be sufficient while maintaining the so luble organic loading rate of 450 g COD/m3d. The HRT higher than 3 days should be applied for soluble organic loading rates higher than 450 g COD/m3d. No adverse effect of COD: S04 between 5 and 20 was found on overall COD removal performance of anaerobic pond operated with OLR of 150 to 600 g COD/m3d. The APs achieve dual purpose of sedimentation of particulate matter and anaerobic conversion 'of organics. As a result settlement of biodegradable suspended solids plays an important role for their accumulation in the sediments. Accordingly, a separate settling column experiment with wastewater from starch factory revealed that a settling time of approximately 120 min is sufficient to remove 90-95% of the influent TSS. Besides settling of suspended solid5, a considerable amount of biological organic matter conversion to methane occurs in bulk liquid layer of anaerobic pond. Bulk liquid contribution to produce methane was found from 9.5 to 26% of total methane formation in anaerobic ponds at OLR between 150 to 600 g COD/m3d. Tracer studies, using Lithium chloride as a tracer in lab-scale anaerobic pond were carried out to investigate the hydraulic behavior. Increase of OLR in anaerobic pond influence the mixing characteristics of the pond as evidenced by the increase~ in dispersion number. Sludge activity tests were performed on sludge obtained from sediment layer as well as from bulk liquid layer of three different sources viz. lab-scale column in series reactors, lab-scale rectangular anaerobic ponds and full-scale anaerobic pond. It was also observed that at same operating condition both the sludge obtained from sediment and bulk liquid layer posses about the same SMA and SSA. Higher activity was achieved for the sludge obtained from the reactor operated at higher organic loading rates. The SMA of 0.03 to 0.3 g CH4- COD/ g VSS.d and SSA of 0.02 to 0.16 g S04/ g VSS.d at 30 °C was obtained. Batch experiment was carried out at 30°C temperature controlled room to estimate the kinetic coefficient of MPA and SRB. The specific growth rates (μmax) and biomass yield coefficient (Y) for MPA was estimated to be 0.102 -<1 and 0.188 g VSS/ g COD respectively. For SRB the corresponding values estimated to be .0.112 -<1 and 0.141 g VSS/ g S04• Fitting the simulated results of Monod kinetic model to the experimental results yielded the substrate affinity (ks) of 370 mg COD/I for MPA and 25 mg CODI 1 for SRB. The sulfate affinity k504 value of 35 mg S04/l was yielded for SRB. Modeling: Mathematical models to simulate the performance of anaerobic pond were developed incorporating both settling of patticulate component and biological anaerobic digestion process. The model considers the anaerobic pond comprises of series of equal size columns. Each column has three compartment viz. liquid layer, active sediment layer and inert sediment layer. The model was transferred to a computer program using VisSim Basic software. The model was verified by comparing simulated results with full-scale as well as with lab-scale anaerobic pond performance. A good agreement between the simulated and the observed pond performance was achieved. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-04-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Annachhatre, Ajit P.; |
| Examination Committee(s) | Chongrak Polprasert; Malinen, Raimo O.;Vase, Jean Luc; |
| Scholarship Donor(s) | Danish International Development Assistance (Danida); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |