Chakkrid Sattayatewa

Effect of oxic and anoxic conditions on nitrous oxide emissions from nitrification and denitrification processes

A lab‐scale sequencing batch reactor fed with real municipal wastewater was used to study nitrous oxide (N2O) emissions from simulated wastewater treatment processes. The experiments were performed under four different controlled conditions as follows: (1) fully aerobic, (2) anoxic–aerobic with high dissolved oxygen (DO) concentration, (3) anoxic–aerobic with low DO concentration, and 4) intermittent aeration. The results indicated that N2O production can occur from both incomplete nitrification and incomplete denitrification. N2O production from denitrification was observed in both aerobic and anoxic phases. However, N2O production from aerobic conditions occurred only when both low DO concentrations and high nitrite concentration existed simultaneously. The magnitude of N2O produced via anoxic denitrification was lower than via oxic denitrification and required the presence of nitrite. Changes in DO, ammonium, and nitrite concentrations influenced the magnitude of N2O production through denitrification. The results also suggested that N2O can be produced from incomplete denitrification and then released to the atmosphere during aeration phase due to air stripping. Therefore, biological nitrogen removal systems should be optimized to promote complete nitrification and denitrification to minimize N2O emissions. Biotechnol. Bioeng. 2011;108:2036–2045.

Organic nitrogen transformations in a 4-stage Bardenpho nitrogen removal plant and bioavailability/biodegradability of effluent DON.

Nitrogen species, specifically, the fate and occurrence of organic nitrogen (ON) within a 4-stage Bardenpho process bioreactor producing low total nitrogen (TN) effluents were investigated in this study. The results showed release of ON in primary anoxic zone and no ON release in the first aerobic zone of the process. The research included investigation of biodegradability/bioavailability of wastewater-derived effluent dissolved ON (DON). The final-effluent DON utilization was evaluated by two different bioassay protocols in the presence and absence of nitrate. About 28-57% of the effluent DON was bioavailable/biodegradable. Bioavailable (to algae and bacteria) DON (ABDON) and biodegradable (to bacteria) DON (BDON) results did not show significant differences in terms of quantity, but DON utilization rates by ABDON (0.13 day(-1)) protocol were higher than that of the BDON (0.04 day(-1)) protocol in the nitrate-removal samples. As a result, ABDON requires a shorter time to exert the bioavailable fraction due to symbiotic relationship between algae and bacteria. In the nitrate-containing samples, it appears that nitrate competes with labile DON as a nitrogen source to microorganisms in both ABDON and BDON protocols. The first order decay rate of DON in the presence of nitrate was 0.11 day(-1) and 0.02 day(-1) for ABDON and BDON, respectively.

Fate of organic nitrogen in four biological nutrient removal wastewater treatment plants.

This study investigated the fate of nitrogen species, especially organic nitrogen, along the mainstream wastewater treatment processes in four biological nutrient removal (BNR) wastewater treatment plants (WWTPs). It was found that the dissolved organic nitrogen (DON) fraction was as high as 47% of soluble nitrogen (SN) in the low-SN effluent plant, which limited the plants capability to remove nitrogen to very low levels. A lower DON fraction was observed in high-SN effluent plants. Effluent DON concentrations from the four plants ranged from 0.5 to 2 mg N/L and did not vary significantly, even though there was a large variation in the influent organic nitrogen concentrations. Size fractionation of organic nitrogen by serial filtration through 1.2-, 0.45-, and 0.22-microm pore-sized membrane filters and the flocculation-and-filtration with zinc sulfate (ZnSO4) method was investigated. The maximum colloidal organic nitrogen (CON) fractions found were 68 and 45% in the primary effluent and final effluent, respectively. The experimental results showed that effluents after filtration through the 0.45-microm pore-sized filter contain significant colloidal fractions; hence, the constituents, including organic nitrogen, are not truly dissolved. A high CON fraction was observed in wastewater influents and was less significant in effluents. The flocculation and filtration method removed the colloidal fraction; therefore, the true DON fraction can be determined.

Odor Emission Rate Estimation of Indoor Industrial Sources Using a Modified Inverse Modeling Method

ABSTRACT Odor emission rates are commonly measured in the laboratory or occasionally estimated with inverse modeling techniques. A modified inverse modeling approach is used to estimate source emission rates inside of a postdigestion centrifuge building of a water reclamation plant. Conventionally, inverse modeling methods divide an indoor environment in zones on the basis of structural design and estimate source emission rates using models that assume homogeneous distribution of agent concentrations within a zone and experimentally determined link functions to simulate airflows among zones. The modified approach segregates zones as a function of agent distribution rather than building design and identifies near and far fields. Near-field agent concentrations do not satisfy the assumption of homogeneous odor concentrations; far-field concentrations satisfy this assumption and are the only ones used to estimate emission rates. The predictive ability of the modified inverse modeling approach was validated with measured emission rate values; the difference between corresponding estimated and measured odor emission rates is not statistically significant. Similarly, the difference between measured and estimated hydrogen sulfide emission rates is also not statistically significant. The modified inverse modeling approach is easy to perform because it uses odor and odorant field measurements instead of complex chamber emission rate measurements. IMPLICATIONS Emission rates of odor and odorant sources are used to assess and predict indoor environmental quality. The modified inverse modeling approach is an efficient, effective, and validated method for estimating emission rates using only odor and odorant concentrations measured indoors in the postdigestion centrifuge building of a water reclamation plant. The modified inverse modeling approach provides an easier method to predict odor and odorant emission rates in an indoor industrial environment than the conventional complex approach that simulates field conditions and then measures odor and odorant concentrations in the laboratory.

A methodological approach for assessing indoor occupational risk from odor perception

This paper combines risk assessment principles with odor measurement concepts to develop a risk management tool that assists water reclamation plants’ administrators to identify, predict, and interpret the magnitude of risk associated with occupational odor perception. Analogous to the noncarcinogenic hazard index, an Odor Hazard Index (OHI) was formulated based on an Odor Reference Concentration (ORfC), which is a new concept similar to the widely used Reference Concentration (RfC) for inhalation exposures to chemicals. The OHI equals to the ratio of observed odor concentration over the ORfC, and sets a new acceptable level of odor perception, which specifies that 80% of building occupants do not perceive the odor. As the OHI approaches unity, concern about negative responses to odor perception increases. The OHI was estimated using a database generated in the dewatering building of a large water reclamation plant and was applied to evaluate odor levels and their perception at conditions with and without an odor control strategy. The control strategy was assessed using AERMOD model estimations of H2S outdoor concentrations to assure that it did not impact surrounding residential areas. The OHI responds to research limitations of odor risk assessment and management, and helps determine if a particular control strategy reduces indoor odors to acceptable levels. The risk management component of this study verified that outdoor acute and long-term ambient H2S standards are not violated as a result of the control strategy implemented by this work.

Case study of odor and indoor air quality assessment in the dewatering building at the Stickney Water Reclamation Plant

Indoor air quality (IAQ) and odors were determined using sampling/monitoring, measurement, and modeling methods in a large dewatering building at a very large water reclamation plant. The ultimate goal was to determine control strategies to reduce the sensory impacts on the workforce and achieve odor reduction within the building. Study approaches included: (1) investigation of air mixing by using CO(2) as an indicator, (2) measurement of airflow capacity of ventilation fans, (3) measurement of odors and odorants, (4) development of statistical and IAQ models, and (5) recommendation of control strategies. The results showed that air quality in the building complies with occupational safety and health guidelines; however, nuisance odors that can increase stress and productivity loss still persist. Excess roof fan capacity induced odor dispersion to the upper levels. Lack of a local air exhaust system of sufficient capacity and optimum design was found to be the contributor to occasional less than adequate indoor air quality and odors. Overall, air ventilation rate in the building has less effect on persistence of odors in the building. Odor/odorant emission rates from centrifuge drops were approximately 100 times higher than those from the open conveyors. Based on measurements and modeling, the key control strategies recommended include increasing local air exhaust system capacity and relocation of exhaust hoods closer to the centrifuge drops.