The effect of aeration rate on nutrient removal from slaughterhouse wastewater was examined in two 10-L laboratory-scale sequencing batch reactors (SBRs--SBR1 and SBR2) operated at ambient temperature. The contaminants in the slaughterhouse wastewater had average concentrations of 4,000 mg chemical oxygen demand (COD) L⁻¹, 350 mg total nitrogen (TN) L⁻¹ and 26 mg total phosphorus (TP) L⁻¹. The duration of a complete SBR operation cycle was 8 h and comprised four operational phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactors were intermittently aerated four times at 50-min intervals, 50 min each time. DO, pH and oxidation-reduction potential (ORP) in the reactors were real-time monitored. Four aeration rates--0.2 L air min⁻¹ in SBR1 for 70 days, 0.4 L air min⁻¹ in SBR1 for 50 days, 0.8 L air min⁻¹ in SBR2 for 120 days and 1.2 L air min⁻¹ in SBR1 for 110 days--were tested. When the aeration rate was 0.2 L air min⁻¹, the SBR was continuously anaerobic. When the aeration rate was 0.4 L air min⁻¹, COD and TP removals were 90% but TN removal was only 34%. When the aeration rates were 0.8 and 1.2 L air min⁻¹, average effluent concentrations were 115 mg COD L⁻¹, 19 mg TN L⁻¹ and 0.7 mg TP L⁻¹, giving COD, TN and TP removals of 97%, 95% and 97%, respectively. It was found that partial nitrification followed by denitrification occurred in the intermittently aerated SBR systems.

Two series of laboratory-scale vertical flow systems (flooded and nonflooded columns) were designed to compare nitrogen removal performance, nitrous oxide emission, and ammonia volatilization under different water levels upon treating diluted digested livestock liquid. In these systems, influent was supplied at three hydraulic loading rates (HLRs of 1.25, 2.5, and 5 cm day⁻¹) during stage 1 and the rates were doubled during stage 2 when the water levels of nonflooded columns were elevated from zero to half the height of the soil column. After hydraulic loading rates doubled, the average removal rates of total nitrogen in flooded columns varied from 1.27 to 2.94 g⁻² day⁻¹ and those in nonflooded columns ranged from 1.23 to 3.88 g⁻² day⁻¹. The T-N removal at an HLR of 10 cm day⁻¹ in the nonflooded column with an elevated water table level had higher efficiency than that in the flooded column, suggesting T-N removal is enhanced in the nonflooded column probably due to the improved coupled nitrification–denitrification process under the elevated water table level condition. On the other hand, there was a significant correlation (r ² = 0.532, p < 0.001) between the N₂O flux and redox potential that mainly corresponded to water levels and HLRs, suggesting anoxic or aerobic conditions stimulate N₂O emission by enhancing the nitrification (nitrification–denitrification) process. In contrast, NH₃ volatilization had a high flux in the anaerobic condition mainly because of flooding. Based on the experimental results, it is hypothesized a nonflooded condition with higher water table level (Eh range of −160 to +260 mV) would be suitable to reduce N₂O emission and NH₃ volatilization peak value by at least half while maintaining relatively efficient nitrogen removal performance.

A conceptual model of solute transport with bioremediation processes using sawdust as a matrix to improve the efficiency of bioremediation in porous media is presented. The transport part of the model solves the advection dispersion differential equations and the reaction part describes the heterotrophic metabolisms of several groups of bacteria. The bacterial growth is formulated using the double Monod kinetic equation. The model depicts the utilization of oxygen, nitrate, manganese, iron oxides and sulfate as electron acceptors for oxidation of organic carbon in porous media. Exchange between the different phases (mobile pore water phase, bio phase and matrix phase) is also considered in this model. Model parameters were adopted from literature on bioremediation processes. Feasibility and applicability of parameters were assessed by conducting a laboratory soil-sawdust columns experiments and comparing the simulated results with the experimental data. The results indicate that sawdust could be employed as low-cost materials to enhance the bioremediation processes in porous media. While the availability of organic carbon is one of the most important factors that affect bacterial activity in porous media, this study demonstrates that using sawdust as a carbon source can improve the bacterial activity and increase the column permeability.

Littoral zones are characterized by gradients in depth and vegetation biomass, influencing nutrient retention capacity. A field experiment was conducted in a Phragmites australis dominated littoral zone to investigate nutrient retention and its effect on surface water quality. Measurements were done in mesocosms where water levels could be manipulated. Nutrient status was investigated along a gradient perpendicular to the shore during two growing seasons, one with a stable water level and one with a gradually decreasing water level. Nutrient concentrations in sediment, soil pore water and surface water were significantly lower in the vegetated than in the unvegetated zone. The negative correlations of nutrients in sediment and water, with nutrient contents of the vegetation suggest a direct effect of the vegetation. Nutrient uptake and biomass of the vegetation was higher in continuously flooded soils than in seasonally emerging sediments higher along the littoral gradient, probably due to the increased salinity in drained zones. Denitrification rate was highest in the unvegetated zone and was positively related to water level. Flooded littoral zones did result in a higher nutrient retention than drained zones. On small scale, for an optimal nutrient retention a fluctuating regime is not necessarily better suited than a stable water level, but on a larger scale it can substantially increase the width of the vegetated zone. It is important to optimize conditions for helophyte growth since the positive effect of vegetation on nutrient retention, at least at local scale, has been demonstrated in this study.