Leachate water quality of soils amended with different swine manure-based amendments.

In the face of the rising level of manure production from concentrated animal feeding operations (CAFOs), management options are being sought that can provide nutrient recycling for plant growth and improved soil conditions with minimal environmental impacts. Alternatives to direct manure application are composting and thermochemical conversion which can destroy pathogens and improve handling and storage. The effect of four forms of swine manure-based soil amendments (raw, compost, hydrochar, and pyrochar) on soil fertility and leachate water quality characteristics of a sandy soil were investigated in soil incubation experiments. All four amendments significantly increased soil carbon, cation exchange capacity and available nutrient contents of the soil. However, hydrochar amended soil leached lower amounts of N, P, and K compared to the other amendments including the control. On the other hand, pyrochar amended soil leached higher concentrations of P and K. Subsequent tests on the hydrochar for K and N adsorption isotherms and surface analysis via XPS suggested that these nutrients were not sorbed directly to the hydrochar surface. Although it is still not clear how these nutrients were retained in the soil amended with hydrochar, it suggests a great potential for hydrochar as an alternative manure management option as the hydrochar can be soil applied while minimizing potential environmental issues from the leaching of high nutrient concentrations to water bodies.

Evaluation of oxygen transfer efficiency under process conditions using the dynamic off-gas method.

The off-gas method can be used to investigate standard oxygen transfer efficiencies under process conditions (alphaSOTE) over the operating life of an aeration system. A method to evaluate alphaSOTE is described in detail by US and German standards. The standards, however, do not describe how to evaluate dynamic changes in aSOTE over a day, which can be useful to uncover problems and unfavourable process conditions. Based on over three years experience gained in off-gas testing in Berlin wastewater treatment plants (WWTPs) under operating conditions, a method to evaluate and interpret the dynamic changes in oxygen transfer is presented. The application of the dynamic off-gas method brings important additional information, which can be used to increase operational efficiency of the aeration basin and to increase process reliability, with a relatively small increase in effort. This paper shows how to perform dynamic measurements under process conditions. Some results of such measurements under dynamic process conditions, performed in a Berlin WWTP, are discussed.

Evaluation of ceramic and membrane diffusers under operating conditions with the dynamic offgas method.

The aeration systems of two full-scale, activated-sludge basins were compared during a period of three years, under the same operating conditions, using dynamic offgas testing. Only the material of the diffuser was different (membrane versus ceramic-tube diffusers). The investigation has shown that, although the membrane diffusers have higher initial standard-oxygen-transfer efficiency (alphaSOTE) and standard-aeration efficiency (alphaSAE), these decreased over time, while the alphaSAE of the ceramic diffusers started lower, but increased slightly over the whole period. A cost comparison makes clear how important it is to evaluate the aeration system under process conditions. The operating costs were the dominant factor (approximately 10x higher than capital costs), and operating costs were approximately 20% higher for membrane versus ceramic diffusers. The poor performance of the membrane-tube diffusers under process conditions could be explained on the basis of the actual alphaAE values in the basin, not the standardized values.

Potential of OUR and OTR measurements for identification of activated sludge removal processes in aerated basins.

In order to develop a process control scheme to reduce energy costs for aeration in activated sludge systems with biological P removal, pre-denitrification and nitrification stages, the spatial distribution of carbon oxidation and nitrification was evaluated over a long full-scale plug flow aeration basin using an externally measured specific oxygen uptake rate (sOUR) and in basin measurement of the actual specific oxygen transfer rate (sOTR) with off-gas testing as well as with the calculated oxygen demand from NH4-N concentrations (sOTR(N)). Using a simple static model, a gas phase balance on oxygen and carbon dioxide, sOTR(N) values were also calculated from off-gas testing. Comparison of sOTR(N) to sOTR and sOUR for carbon oxidation (sOUR(C)) to nitrification (sOUR(N)) at different loading conditions allowed the oxidation processes to be followed over the three zones of the aeration basin. As expected, the distribution depended on the dissolved oxygen concentration (DO) in the basin. However, the major change was in the C-oxidation rate and not the nitrification rate. At a low DO, and when NH4-N was present in the zone, the amount of oxygen transferred for nitrification was nearly the same, but the overall sOTR was lower. The externally measured sOUR was only useful when it was differentiated into sOUR(N) and sOUR(C). sOUR(N) could be used to predict the nitrification rate in the basin. With further refinement, the gas phase balance model has potential to be used to monitor the degree of nitrification over the basin length. This can be integrated into a control scheme to reduce aeration costs by adjusting the DO setpoint according to loading conditions in the

A control strategy for reducing aeration costs during low loading periods.

The efficiency of the aeration system in a full-scale activated sludge basin with 3 separately controlled aeration zones was improved for the low loading period in summer. The air flow rate to each aeration zone is currently regulated to hold a preset dissolved oxygen concentration (DO). Four different DO setpoint combinations were tested, each one for a one week period, using dynamic off-gas testing to measure the standardised oxygen transfer efficiency (alphaSOTE). As the DO setpoints were lowered, the total air flow rate to the basin decreased initially. A low DO in the first zones slowed biomass activity and pushed the load towards the end of the aeration basin. The relationship between alphaSOTE and the specific diffuser flow rate qD is different for each zone. In Zone 1 there was a strong decrease in alphaSOTE as qD increased, while Zones 2 and 3 were fairly independent of qD, Zone 2 at a higher level than Zone 3. Aeration costs were reduced by 15% for the most efficient combination. To achieve even more savings, a control strategy adjusting oxygen transfer rates over the aeration basin to the necessary oxygen transfer rates is suggested. It is based on changing the DO setpoints to reach the lowest total air flow rate while meeting the effluent requirements.

Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation.

A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.

Comparison of the efficiency of large-scale ceramic and membrane aeration systems with the dynamic off-gas method.

The aeration systems of two full-scale activated sludge basins were compared over 2.5 years under the same operating conditions using dynamic off-gas testing. Only the material of the diffuser was different, membrane vs. ceramic tube diffusers. The experimental design took the complexity and dynamics of the system into consideration. The investigation has shown that, although the membrane diffusers have higher initial standard oxygen transfer efficiency (SOTE) and standard aeration efficiency (SAE), these decreased over time, while the SAE of the ceramic diffusers started lower, but increased slightly over the whole period. Measurement of air distribution in the basins along with dissolved oxygen concentration profiles have provided important information on improving process control and reducing energy costs. The results show that dynamic off-gas testing can effectively be used for monitoring the aeration system and to check design assumptions under operating conditions. The information can be used to improve the design of new aeration systems or in retro-fitting existing basins.

Kinetics of decolorization and mineralization of the azo dye reactive black 5 by hydrogen peroxide and UV light.

C.I. Reactive Black 5 is one of the most used reactive dyes for textile finishing. It is a diazo dye, which can be decolorized by facultative anaerobic bacteria, sulfate reducing bacteria and aerobic white rot fungi. Mineralization by microorganisms has proven difficult. Advanced oxidation processes are promising alternatives for the decolorization and mineralization of Reactive Black 5, alone and in combination with aerobic biodegradation. The kinetics of the decolorization of Reactive Black 5 using a combination of hydrogen peroxide and UV radiation have been investigated. The rate of decolorization is first order with respect to dye concentration. It is enhanced with increasing hydrogen peroxide concentrations up to an optimum value. In our model we have correlated an empirical reaction rate expression which considers the contribution of both hydrogen peroxide and UV flux radiation based on the reaction kinetics. This empirical correlation agrees well with the experimental data for these conditions. Complete decolorization corresponded with 40-50% mineralization of the dye. Further mineralization can be achieved with extended radiation time.

Decolorization of reactive dyes by the white rot fungus Trametes versicolor in sequencing batch reactors.

The white rot fungus Trametes versicolor was shown to be capable of decolorizing three reactive dyes in a sequencing batch process, using glucose as the carbon and energy source over an extended period without supplementation of new mycelium. Decolorization activity was related to the expression of extracellular peroxidases and could be continuously reactivated by sheering the suspended pellets. Pure culture experiments were carried out simultaneously in agitated Erlenmeyer flasks and in completely stirred tank reactors with two azo dyes, C.I. Reactive Black 5 and C.I. Reactive Red 198 as well as the anthraquinone dye C.I. Reactive Blue 19 (Brilliant Blue R). Results show high and stable degrees of decolorization of 91%-99% in both systems, which could be repeated without decrease in activity over time. Under nonsterile conditions only five cycles of decolorization could be achieved. An increasing bacterial population suppressed fungal growth and the formation of peroxidases.