Dimitrios V. Vayenas

Removal of Mn and simultaneous removal of NH3, Fe and Mn from potable water using a trickling filter

Manganese removal using a biological trickling filter was investigated. Manganese removal was found to be caused by both biological and chemical manganese oxidation. The extent of each oxidation type was assessed. The performance of the trickling filter was tested under both continuous and sequencing batch reactor operation. The effectiveness and throughput for each operational mode were determined as a function of retention time and the advantages of each operational mode were investigated. It was found that the continuous operational mode leads to higher percentage of manganese removal but lower throughput rates when compared with a sequencing batch reactor operation with the same feed concentration and retention time. A series of experiments was also performed in order to investigate the interactions between ammonia, iron and manganese removal when simultaneously present in a biological filter. For low ammonia concentrations there is no serious inhibition of manganese removal. For higher ammonia concentrations inhibition of manganese removal becomes substantial. The presence of iron affects both ammonia and manganese removal negatively, while ammonia and manganese do not significantly affect iron removal.

Removal of iron from potable water using a trickling filter

A trickling filter for iron removal from potable water has been constructed and tested. Iron removal was found to be caused by both biological and physico-chemical iron oxidation. The extent of each oxidation type was assessed. In addition, iron concentration profiles were taken along the filter depth, for both biological and physico-chemical iron oxidation, under the same operating conditions. Significant quantities of iron precipitated, mandating a periodic filter backwash. The possible duration of the filter operating cycles was studied as a function of the inlet iron concentration and the volumetric flow-rate. The limits of feed iron concentration and hydraulic loadings on the filter were determined and appropriate operating diagrams were constructed.

Development of a dynamic model describing nitritification and nitratification in trickling filters

A dynamic model which describes nitritification and nitratification in trickling filters has been developed. The model predicts the concentration profiles of ammonia, nitrite and nitrate along the filter depth and along the biofilm depth, as a function of the operating parameters, in batch as well as in continuous operation. The model can also predict the biofilm thickness as a function of filter depth and time. The batch version of the model predicts that the best moment to start the continuous operation is the moment when Nitrobacter concentration is maximum and nitrite concentration is minimum, while the continuous version of the model predicts that nitrite accumulation would be observed only when a significant ammonia concentration is observed at the filter outlet. A pilot-scale trickling filter was used in order to verify the predicted results. In all cases there was very good agreement between predicted and experimental results.

Integrated Cr(VI) removal using constructed wetlands and composting.

The present work was conducted to study integrated chromium removal from aqueous solutions in horizontal subsurface (HSF) constructed wetlands. Two pilot-scale HSF constructed wetlands (CWs) units were built and operated. One unit was planted with common reeds (Phragmites australis) and one was kept unplanted. Influent concentrations of Cr(VI) ranged from 0.5 to 10mg/L. The effect of temperature and hydraulic residence time (8-0.5 days) on Cr(VI) removal were studied. Temperature was proved to affect Cr(VI) removal in both units. In the planted unit maximum Cr(VI) removal efficiencies of 100% were recorded at HRTs of 1 day with Cr(VI) concentrations of 5, 2.5 and 1mg/L, while a significantly lower removal rate was recorded in the unplanted unit. Harvested reed biomass from the CWs was co-composted with olive mill wastes. The final product had excellent physicochemical characteristics (C/N: 14.1-14.7, germination index (GI): 145-157%, Cr: 8-10mg/kg dry mass), fulfills EU requirements and can be used as a fertilizer in organic farming.

Molasses as an efficient low-cost carbon source for biological Cr(VI) removal

In the present study, indigenous microorganisms from industrial sludge were used to reduce the activity of Cr(VI). Molasses, a by-product of sugar processing, was selected as the carbon source (instead of sugar used in a previous work) as it is a low-cost energy source for bioprocesses. Initially, experiments were carried out in suspended growth batch reactors for Cr(VI) concentrations of 1.5-110 mg/L. The time required for complete Cr(VI) reduction increased with initial Cr(VI) concentration. Initial molasses concentration was also found to influence the Cr(VI) reduction rate. The optimal concentration for all initial Cr(VI) concentrations tested was 0.8 gC/L. Experiments were also carried out in packed-bed reactors. Three different operating modes were used to investigate the optimal performance and efficiency of the filter, i.e. batch, continuous and SBR with recirculation. The latter mode with a recirculation rate of 0.5L/min lead to significantly high Cr(VI) reduction rates (up to 135 g/m(2)d). The results of this work were compared with those of a similar work using sugar as the carbon source and indicate that molasses could prove a feasible technological solution to a serious environmental problem.

On the design of nitrifying trickling filters for potable water treatment

Abstract A practical graphical method for the design of nitrifying trickling filters for potable water treatment is presented. The method allows the selection of the key design parameters (support media and filter dimensions) based on appropriate design curves. In the sequel, the possible advantages of water recirculation are examined theoretically and experimentally. Both theoretical and experimental results shown that an increase in ammonia bioconversion is expected for high or intermediate values of hydraulic loading and high values of inlet ammonia concentration, whereas at low hydraulic rates, recirculation has an adverse effect.

Mathematical modeling of olive mill waste composting process

The present study aimed at developing an integrated mathematical model for the composting process of olive mill waste. The multi-component model was developed to simulate the composting of three-phase olive mill solid waste with olive leaves and different materials as bulking agents. The modeling system included heat transfer, organic substrate degradation, oxygen consumption, carbon dioxide production, water content change, and biological processes. First-order kinetics were used to describe the hydrolysis of insoluble organic matter, followed by formation of biomass. Microbial biomass growth was modeled with a double-substrate limitation by hydrolyzed available organic substrate and oxygen using Monod kinetics. The inhibitory factors of temperature and moisture content were included in the system. The production and consumption of nitrogen and phosphorous were also included in the model. In order to evaluate the kinetic parameters, and to validate the model, six pilot-scale composting experiments in controlled laboratory conditions were used. Low values of hydrolysis rates were observed (0.002841/d) coinciding with the high cellulose and lignin content of the composting materials used. Model simulations were in good agreement with the experimental results. Sensitivity analysis was performed and the modeling efficiency was determined to further evaluate the model predictions. Results revealed that oxygen simulations were more sensitive on the input parameters of the model compared to those of water, temperature and insoluble organic matter. Finally, the Nash and Sutcliff index (E), showed that the experimental data of insoluble organic matter (E>0.909) and temperature (E>0.678) were better simulated than those of water.

Constructed wetlands in the treatment of agro-industrial wastewater: A review

Due to their simplicity and low operation cost, constructed wetlands are n becoming more prevalent in wastewater treatment all over the world. Their n range of applications is no longer limited to municipal wastewater but has n expanded to the treatment of heavily polluted wastewaters such as n agro-industrial effluents. This paper provides a comprehensive literature n review of the application of constructed wetlands in treating a variety of n agro-industrial wastewaters, and discusses pollutant surface loads and the n role of constructed wetland type, prior-treatment stages and plant species in n pollutant removal efficiency. Results indicate that constructed wetlands can n tolerate high pollutant loads and toxic substances without losing their n removal ability, thus these systems are very effective bio-reactors even in n hostile environments. Additionally, the review outlines issues that could n improve pollutant treatment efficiency and proposes design and operation n suggestions such as suitable vegetation, porous media and constructed wetland n plain view. Finally, a decision tree for designing constructed wetlands n treating agro-industrial wastewaters provides an initial design tool for n scientists and engineers.

Biological Cr(VI) removal using bio-filters and constructed wetlands.

The bioreduction of hexavalent chromium from aqueous solution was carried out using suspended growth and packed-bed reactors under a draw-fill operating mode, and horizontal subsurface constructed wetlands. Reactors were inoculated with industrial sludge from the Hellenic Aerospace Industry using sugar as substrate. In the suspended growth reactors, the maximum Cr(VI) reduction rate (about 2 mg/L h) was achieved for an initial concentration of 12.85 mg/L, while in the attached growth reactors, a similar reduction rate was achieved even with high initial concentrations (109 mg/L), thus confirming the advantage of these systems. Two horizontal subsurface constructed wetlands (CWs) pilot-scale units were also built and operated. The units contained fine gravel. One unit was planted with common reeds and one was kept unplanted. The mean influent concentrations of Cr(VI) were 5.61 and 5.47 mg/L for the planted and unplanted units, respectively. The performance of the planted CW units was very effective as mean Cr(VI) removal efficiency was 85% and efficiency maximum reached 100%. On the contrary, the unplanted CW achieved very low Cr(VI) removal with a mean value of 26%. Both attached growth reactors and CWs proved efficient and viable means for Cr(VI) reduction.

Operational and Design Considerations of a Trickling Filter for Ammonia Removal from Potable Water

We studied the steady-state behavior of a mathematical model of a nitrifying trickling filter. In particular, we studied the effect of the operating conditions of the filter on the complete and safe nitrification. We presented the results with the help of the operating diagram of the system and we determined the range of operating conditions resulting in optimal operation. We also computed biofilm thickness along the filter depth and concentration profiles inside the biofilm, and compared them with experimental results found in the literature. The comparison shows very good qualitative agreement between model predictions and experimental data.