Jiajie He

Municipal wastewater treatment through an aerobic biofilm SBR integrated with a submerged filtration bed

A biofilm reactor and a gravitational filtration bed were integrated as a sequencing batch reactor (SBR) to aerobically treat a municipal wastewater. Polyacrylonitrile balls (50 mm diameter, 90% porosity) were filled into the upper part of the SBR as biofilm attaching materials and anthracite coal (particle size approximately 1.17 mm) was placed into the lower part as filter media. The SBR was aerated during filling and reaction phases, followed by a 10 min discharge phase during which the wastewater went through the filtration bed without aeration. The SBR was tested with raw wastewater from a municipal WWTP in Wuhan, China from July 2006 to January 2007, during both a warm season and a cold season. The SBR showed a capability to accept COD and turbidity fluctuations in the receiving wastewater. Seasonal influence on COD and nitrogen removal by the biofilm reactor was significant. Nitrogen and phosphorus removals were limited by COD levels in the wastewater. The filtration process removed considerable COD, nitrogen, phosphorus, and turbidity. The overall SBR effluent quality consistently satisfied the national secondary effluent discharge standard of China, except for total phosphorus. An anaerobic phase before the aerobic reaction is proposed to improve phosphorus and nitrogen removal. The filter normally required a backwash every seven days and the water needed for backwash was less than 4% of the wastewater treated by the SBR. This experiment provides information needed for further investigation to improve performance of the SBR.

Hydraulic management of a soil moisture controlled SDI wastewater dispersal system in an Alabama Black Belt soil

Rural areas represent approximately 95% of the 14000 km(2) Alabama Black Belt, an area of widespread Vertisols dominated by clayey, smectitic, shrink-swell soils. These soils are unsuitable for conventional onsite wastewater treatment systems (OWTS) which are nevertheless widely used in this region. In order to provide an alternative wastewater dosing system, an experimental field moisture controlled subsurface drip irrigation (SDI) system was designed and installed as a field trial. The experimental system that integrates a seasonal cropping system was evaluated for two years on a 500-m(2) Houston clay site in west central Alabama from August 2006 to June 2008. The SDI system was designed to start hydraulic dosing only when field moisture was below field capacity. Hydraulic dosing rates fluctuated as expected with higher dosing rates during warm seasons with near zero or zero dosing rates during cold seasons. Lower hydraulic dosing in winter creates the need for at least a two-month waste storage structure which is an insurmountable challenge for rural homeowners. An estimated 30% of dosed water percolated below 45-cm depth during the first summer which included a 30-year historic drought. This massive volume of percolation was presumably the result of preferential flow stimulated by dry weather clay soil cracking. Although water percolation is necessary for OWTS, this massive water percolation loss indicated that this experimental system is not able to effective control soil moisture within its monitoring zone as designed. Overall findings of this study indicated that soil moisture controlled SDI wastewater dosing is not suitable as a standalone system in these Vertisols. However, the experimental soil moisture control system functioned as designed, demonstrating that soil moisture controlled SDI wastewater dosing may find application as a supplement to other wastewater disposal methods that can function during cold seasons.

Partial nitrification of non-ammonium-rich wastewater within biofilm filters under ambient temperature

This study evaluated the partial nitrification performances of two biofilm filters over a synthetic non-ammonium-rich wastewater at a 20°C room temperature under both limited DO (∼2.0 mg/L) and unlimited DO (∼4.0 mg/L) conditions. The two filters were each of 80 cm long and used different biofilm carriers: activated carbon and ceramic granule. Results showed that partial nitrification was accomplished for both filters under the limited DO condition. However, the effluent NO(2)-N was higher in the ceramic granule filter than in the activated carbon filter, and was less susceptible to the influent COD/N changes. Further investigation into the water phase COD and NH(4)-N depth profiles and bacteria population within the two filters showed that by putting upper filter layer (upstream) to confront relatively higher influent COD/N ratios, the filtration process naturally put lower filter layers (downstream) relatively more favorable for nitrifying bacteria (ammonia oxidizing bacteria in this study) to prosper, making the filter depth left for nitrification a crucial factor for the effectiveness of nitrification with a filter. The potentially different porous flow velocities of the two filters might be the reason to cause their different partial nitrification performances, with a lower porous flow velocity (the ceramic granule filter) favoring partial nitrification more. In summation, DO, filter depth, and filtration speed should be played together to successfully operate a biofilm filter for partial nitrification.

Microbial community changes during the start-up of an anaerobic/aerobic/anoxic-type sequencing batch reactor

An anaerobic/aerobic/anoxic-type sequencing batch reactor was started up during a summer rainy season to obtain enhanced biological phosphorus removal (EBPR), and its sludge microbial community was also monitored in the hope of observing the microbial community evolution of polyphosphate-accumulating organisms (PAOs). During the start-up process, a total of 17 bands of highest species richness were detected in the sludge microbial community, including Alpha-, Beta-, and Gamma- Proteobacteria, as well as Actinobacteria and Planctomycetes. Major microbial community structural change was observed in Rhodocyclus-related and Acinetobacter-related PAOs, glycogen-accumulating organisms (GAOs), and Actinobacteria. In contrast to the current belief that enrichment of PAOs is essential for the establishment of EBPR, PAOs were not favourably enriched in this study. Instead, Actinobacteria and GAOs overwhelmingly flourished. The overall conclusion of this study challenges the conventional view that EBPR cannot live without traditional PAOs. However, it suggests an non-negligible role of denitrifying phosphorus-accumulating bacteria in EBPR systems, as well as other uncultured bacteria.

Impact of a real-time controlled wastewater subsurface drip disposal system on the selected chemical properties of a vertisol

The operation of onsite septic effluent disposal without considering seasonal moisture changes in drain field conditions can be a major cause of the failure of conventional septic systems. This study addressed this issue from a soil hydraulic perspective by using real-time drain field soil moisture levels to limit septic effluent disposal in a vertisol via subsurface drip irrigation. A prototype system was field-tested in a Houston clay soil and results describe the subsequent impact on selected soil chemical properties. After one year of hydraulic dosing with a synthetic wastewater, soil total carbon and nitrogen concentrations increased, but no increase in soil total phosphorus concentration was observed. Soil NO3-N leaching potential was noted, but soil NH4-N concentrations decreased, which could be ascribed to NH4-N nitrification, fixation within clay sheets and NH3 volatilization. Soil K+, Mg2+ and Na+ concentrations increased in soil layers above the drip lines, but decreased in soil layers below drip lines. Soil electrical conductivity accordingly increased in soil layers above drip lines, but the range was significantly lower than the threshold for soil salinity. Although the moisture-controlled effluent disposal strategy successfully avoided hydraulic dosing during unfavourable wet drain field conditions and prevented accumulation of soil salts in the soil profile beneath the drip lines, soil salts tended to accumulate in top soil layers. These adverse effects warrant system corrections before large-scale implementation of subsurface drip irrigation of effluent in similar vertisols.

Innovative on-site wastewater alternatives with drip irrigation

A number of Blackland Prairie soils in central Alabama are unsuitable for conventional onsite sewage disposal due to low permeability and seasonal high water tables. After an initial survey of state health department environmentalists, a wastewater drip irrigation test site at the Black Belt Research and Extension Station in Marion Junction, Alabama was selected for study. The experimental site to be installed in summer 2006 is designed to test hydraulic loading rates and plant and crop uptake parameters of drip irrigated wastewater. An innovative system of monitoring and feedback provides volumetric soil moisture control for drip irrigation dosing. The goal of this research is not maximum disposal of waste, rather alternative treatment and beneficial reuse of effluent using an environmentally friendly plant uptake system at sustainable loading rates in marginal soils. Basic research objectives are to quantify sustainable loading rates for on-site sewage disposal in characteristic Blackland Prairie soils with a focus on increasing the natural loading rates of the soil through an integrated cropping/subsurface drip irrigation disposal system.