Richard O. Mines

Misconceptions about Unstirred SVI

Settling characteristics of mixed liquor from a completely-mixed activated sludge process were evaluated in 1-L stirred and unstirred, plastic settling columns in addition to performing the same analyses in 5-L stirred and unstirred settling columns. All analyses were performed in accordance with 1992 Standard Methods. Mixed liquor suspended solids concentrations ranged from approximately 1,200 to 9,400 mg/L. Two-tailed, paired comparison, statistical analyses at the 5% level of significance indicated there was a significant difference between the SVIs obtained from the stirred and unstirred 1-L and 5-L settling columns. Two-tailed, paired comparison, statistical analyses performed at the 5% level of significance indicated there was a significant difference between the zone settling velocities observed in the stirred and unstirred 1-L and 5-L settling columns. Surface areas based on stirred settling column analyses may result in areas that are 33% to 238% smaller then those predicted from unstirred settling column analyses. In the design of full-scale, secondary clarifiers, it is recommended that a scaling factor of 1.5 – 2.0 be applied to the limiting solids flux values obtained from stirred settling column analyses in order for them to handle peak solid loading rates.

Comparison of oxygen transfer parameters and oxygen demands in bioreactors operated at low and high dissolved oxygen levels

ABSTRACT The proper design of aeration systems for bioreactors is critical since it can represent up to 50% of the operational and capital cost at water reclamation facilities. Transferring the actual amount of oxygen needed to meet the oxygen demand of the wastewater requires α- and β-factors, which are used for calculating the actual oxygen transfer rate (AOTR) under process conditions based on the standard oxygen transfer rate (SOTR). The SOTR is measured in tap water at 20°C, 1 atmospheric pressure, and 0 mg L−1 of dissolved oxygen (DO). In this investigation, two 11.4-L bench-scale completely mixed activated process (CMAS) reactors were operated at various solid retention times (SRTs) to ascertain the relationship between the α-factor and SRT, and between the β-factor and SRT. The second goal was to determine if actual oxygen uptake rates (AOURs) are equal to calculated oxygen uptake rates (COURs) based on mass balances. Each reactor was supplied with 0.84 L m−1 of air resulting in SOTRs of 14.3 and 11.5 g O2 d−1 for Reactor 1 (R-1) and Reactor 2 (R-2), respectively. The estimated theoretical oxygen demands of the synthetic feed to R-1 and R-2 were 6.3 and 21.9 g O2 d−1, respectively. R-2 was primarily operated under a dissolved oxygen (DO) limitation and high nitrogen loading to determine if nitrification would be inhibited from a nitrite buildup and if this would impact the α-factor. Nitrite accumulated in R-2 at DO concentrations ranging from 0.50 to 7.35 mg L−1 and at free ammonia (FA) concentrations ranging from 1.34 to 7.19 mg L−1. Nonsteady-state reaeration tests performed on the effluent from each reactor and on tap water indicated that the α-factor increased as SRT increased. A simple statistical analysis (paired t-test) between AOURs and COURs indicated that there was a statistically significant difference at 0.05 level of significance for both reactors. The ex situ BOD bottle method for estimating AOUR appears to be invalid in bioreactors operated at low DO concentrations (<1.0 mg L−1).

Design, Operation, and Analysis of a Biological Sand Filter Using Copper as a Disinfectant

Aqua Clara International (ACI) is a nonprofit organization that uses biological sand filters (BSFs) to provide economical, clean water to families in developing countries. ACI often recommends loading 20 L/d in BSFs in which a brass alloy is included as a disinfectant. A bench-scale study was conducted to investigate the effectiveness of using copper as the disinfectant. Five filters were constructed to compare different arrangements and amounts of copper shavings to a control, Column 1. The control was modeled after ACI design specifications but no metallic disinfectant was included. Columns 2 – 5 were also scaled according to ACI recommendations. Columns 2 and 3 each contained 4.7 g of copper, and Columns 4 and 5 each contained 2.35 g. In columns 2 and 4, copper was placed in a single layer; while in Columns 3 and 5, the copper was dispersed throughout the fine sand. After 31 days of testing, the average removal efficiency for total coliforms in Columns 1 – 5 was 96.5%, 93.9%, 97.4%, 95.4%, and 97.5% respectively. A single, 20 L/d, BSF was constructed with 94 g of copper dispersed throughout the fine sand layer. The average removal efficiency for fecal coliforms and turbidity was 97.3% and 65.7%, respectively.

Mercer on Mission to Malawi, Africa

The Mercer On Mission (MOM) to Malawi, Africa, otherwise known as Team Malawi, consisted of nine undergraduate students and three faculty members from various departments across the university. Team Malawi traveled to Malawi, Africa, spending June 8–28, 2010, performing various activities with Malawians. The projects selected were in response to Millennium Development Goals (MDGs) numbers: #1 Eradicate Extreme Poverty and Hunger and #7 Ensure Environmental Sustainability. Two of the in-country projects involved working with children and staff at an orphanage in Mangochi where a vegetable garden and orchard were constructed and established for food sustenance. A third project in conjunction with the National Herbarium and Botanical Gardens and the Forestry Department, involved the construction, tilling, and potting of seedlings for the establishment of a tree nursery so that the people of Makoli Village can reforest land that has been denuded and deforested by the community. Two additional projects undertaken by the students were: 1) making compost for use at the vegetable garden and orchard and 2) collecting and analyzing water samples from streams and drinking wells to determine the quality of the water used at the Mangochi Orphanage and Educational Training (MOET) and at the Makoli Village, respectively.

Bench-Scale Ozonation of Raw Industrial and Municipal Wastewater

This project involved the design, operation, and testing of a bench-scale ozonation wastewater treatment system. Untreated municipal and industrial wastewater was collected from the influent chamber to the Rocky Creek Wastewater Treatment Plant (WWTP) in Macon, Georgia. The industrial wastewater consisted of paper mill effluent from the Graphic Packaging Plant adjacent to the Rocky Creek WWTP. The Rocky Creek WWTP treats wastewater in an extended aeration activated sludge process. To accomplish this research, a 10-liter clear PVC, semi-batch, bubble column was used to disperse ozone bubbles through a porous diffuser near the bottom of the column. Three 24-hour runs were conducted on each type of wastewater. The ozone was administered at loading rates of 0.60, 4.70, and 9.92 mg O 3 /min, respectively, to 6 liters of either raw municipal or industrial wastewater. The following parameters were measured frequently during each 24-hour run: pH, chemical oxygen demand (COD), ammonia, nitrite, nitrate, phosphorus, conductivity, turbidity, total suspended solids (TSS), volatile suspended solids (VSS), total dissolved solids (TDS), and total volatile solids (TVS). Overall COD removal for the municipal and industrial wastewater averaged 82% and 84%, respectively, whereas, overall TSS removal averaged 83% and 81%, respectively. The ozonation degradation rate constant (K D ) based on TSS destruction ranged from 0.054 hr –1 to 0.072 hr –1 for the municipal wastewater and from 0.017 hr –1 to 0.066 hr –1 for the industrial wastewater.

Bench-Scale Digestion Studies

Four, 1-L bench-scale digesters were operated for 25 days to evaluate the effectiveness of oxygen and ozone on sludge stabilization. Each digester contained waste activated sludge generated from the Rocky Creek Wastewater Treatment Plant (WWTP) in Macon, Georgia. Two of the digesters were sparged with air and the remaining two digesters were sparged with ozone. The following parameters were measured frequently during the bench-scale study: pH, total and soluble chemical oxygen demand (COD), temperature, total and volatile solids, and total suspended and volatile suspended solids. The kinetics of volatile suspended solids (VSS) reduction was determined and average first order degradation constants (K D ) for the aerobic and ozonated digesters were 0.0824 days –1 and 0.108 days –1 respectively, indicating that ozone was more effective at destroying VSS than oxygen. Total chemical oxygen demand (COD) removals averaged 37% and 64%, respectively for the aerobic versus ozonated digesters. Soluble COD (SCOD) concentrations in the digesters increased from 0 to 15.5 mg/L in the aerobic digesters and from 0 to 293.5 mg/L in the ozonated digesters due to solubilization of the biological sludge solids. Approximately 1.82 mg of oxygen was required per mg of total volatile solids (TVS) destroyed. Average ozone dosages observed in this study were 2.6 and 2.8 mg of O 3 per mg of total solids (TS) destroyed for ozonated digesters 1 and 2, respectively.

Modeling the Effect of Ozonation on Acid Yellow 17 Dye in a Semi-Batch Bubble Column

A pilot-scale ozonation process employing a semi-batch column was used to study the removal of acid yellow dye 17 from synthetic wastewater in a semi-batch bubble column. The effect of initial dye concentration on system performance was evaluated. This study utilized an 11.12-L, clear, PVC column that was filled with 8-L of tap water tainted with the acid yellow 17 dye for each experimental run conducted. Ozone was supplied to the system by sparging the gas through three porous stainless steel filters fixed in the reactor 0.15-m from the bottom of the column. The ozone supply rate was held constant at 3.78 L/min. Acid yellow 17 dye concentration (measured as A400), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5) and the quantity of ozone utilized was measured as a function of ozonation time during each experimental run. Results indicate that ozonation is very effective at removing acid yellow 17 dye from synthetic textile wastewater. The biodegradability of the dye in the synthetic wastewater was evaluated by monitoring changes in BOD5 with respect to COD. The initial BOD5:COD ratio was 0.0083 and over time increased by an order of magnitude to a maximum ratio of 0.126 at 30 minutes. These results indicate that the biodegradability of the wastewater increased with an increase in ozonation time. Two-film theory was used to kinetically model the gas-liquid reactions occurring in the reactor. Modeling results indicated that during the first 10 to 15 min of ozonation, the system could be characterized by a fast, pseudo-first order regime. By combining a differential mole balance on the gas phase ozone concentration within the reactor with film theory, this initial period of the ozonation reaction was successfully modeled. With continued ozonation, system kinetics transitioned through a moderate then to a slow regime. Successful modeling of this period required use of a kinetic equation corresponding to a more inclusive condition. Model results are presented. Copyright ASCE 2005 EWRI 2005 Introduction Textile industry wastewater often contains high concentrations of color and therefore poses a wide variety of issues to receiving streams including the introduction of recalcitrant or toxic compounds and a decrease in relative clarity or turbidity. A common treatment for color containing wastewater is ozonation as this type of process has been shown to remove color (Adams and Gorg, 2002) and chemical oxygen demand (COD) (El-Din and Smith, 2002) and to increase the biodegradability (BOD5:COD) of the wastewater (Zhou and Smith, 1997). Acid yellow 17 dye is a common additive found in ordinary household products such as shampoo, bubble bath, shower gel, liquid soap, multi-purpose cleanser, dishwashing liquid and alcoholbased perfumes. As regulations associated with dyestuff are tightened, associated industries are faced with finding economically viable water treatment solutions. Two-film theory (Lewis and Whitman, 1924) is traditionally used to model mass transfer and associated reactions. For simplicity, many reactions are described as either “slow” or “fast” because relatively simple solutions exist for these regimes. For example, for an instantaneous, reversible reaction typified by a Hatta number (Ha) greater than 3, the reaction is assumed “fast” and an analytical solution is available. For a “slow” reaction, (Ha<0.3), it is assumed that the reaction occurs within the bulk fluid and the reaction rate can be determined from standard kinetic theory. Danckwerts (1970) and van Krevelen and Hoftijzer (1948) have developed approximate methods for the transition region characterized by 0.3<Ha<3. The focus of this study can be characterized as follows: 1. to evaluate the effect of ozone on the removal of acid yellow 17 dye from a synthetic wastewater, and 2. to develop a model based on film theory to describe the removal of COD associated with acid yellow 17 dye by ozonation in a semi-batch reactor. Materials and Methods All experiments were conducted in a semi-batch bubble column. The column was fabricated from clear 7.62 cm schedule 40 PVC pipe and was 2.44 m in height. The gas feed was sparged through three stainless steel filters with 10 um porosity. The sparging system entered the side of the reactor 15.24 cm from the bottom of the column. Ozone was produced with the Ozotech, Inc. OZ2BTUSL ozone generator. The air feeding the ozone generator was conditioned using the Power Prep Model Titan (Ozotech, Inc.). The carrier gas flow rate was maintained at a constant of 3.78 L/min resulting in a uniform ozone introduction to the system of 79.2 mg O3/min. Figure 1 shows a schematic of the equipment utilized. Copyright ASCE 2005 EWRI 2005

Bringing Reality into the Classroom

This paper presents seven activities that were implemented in a senior level, undergraduate course in Environmental Engineering to bring reality into the classroom. Each of the activities will be discussed along with student feedback and an assessment of the use of the seven activities will be presented.