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EBR Denitrification: Example Projects

​Various comparisons have been made between the Electro-Biochemical Reactor (EBR) systems and Conventional Bioreactors (CBR). These comparisons span in-house bench, pilot, and full-scale implementations as well as testing comparisons conducted through impartial third parties against most major water treatment technologies. Overall, the EBR technology has shown better efficiencies and kinetics and was the only technology to meet discharge criteria in a third party comparison of eight water treatment technologies. Presented data in the table gives examples of past EBR denitrification projects, corresponding hydraulic retention times (HRT), and average water temperatures. 
*Indicates projects where nitrate was not the main contaminant of concern.

Coal Mining: EBR Denitrification Case Studies

Four wastewaters, obtained from four different British Columbia (B.C.) coal mine drainages (Waters A through D), were treated using bench-scale EBRs. These waters contained elevated concentrations of nitrate-N, ranging from 11 to 170 mg/L. Nitrate-N is a relevant co-contaminant that can interfere with removal of other metals, as it is reduced under slightly higher ORP conditions (higher energy yield for microbes) and it competes with metal oxyanions for electrons. In all four bench tests, nitrate-N was removed to levels below 1 mg/L.
In the pilot-test waters, nitrate-N at 50 mg/L was the main co-contaminant of interest. Data extrapolation indicated that nitrate-N would be reduced to an average of 2 mg/L in the same 3- to 4-hour HRT required for Se removal. ​

Hardrock Mining: EBR Denitrification Case Study

Nitrogen species, such as nitrate and ammonia, are found in these waters mainly due to the leaching of residual blasting compounds and cyanide leaching. 

Pilot testing was performed to compare the denitrification performance of an existing Conventional Bioreactor facility with the EBR.
The figure above shows nitrate-N + nitrite-N (N+N) removal obtained with the existing Conventional Bioreactor (BR) facility over a 27-month period. The discharge limit of 10 mg/L was met seasonally, during the warmer months. All three BR bioreactors (HRT of 42 hours) were needed to remove N+N from approximately 300 mg/L influent nitrate-N to below the discharge criteria of 10 mg/L.
The pilot-scale EBR nitrate-N removal is shown above. Total HRT of the system was 16 hours, with 8 hours per EBR reactor. The pilot-study ran 3-months and included validation testing followed by stress testing using reduced nutrient additions and low temperatures.  Each of the stress tests, represented by vertical lines on the figure above, influenced the performance of the first-stage EBR (EBR1), but not the second stage EBR (EBR2). During the duration of the pilot-scale tests, second-stage EBR (EBR2) removed influent N+N (nitrate-N at ~300 mg/L) to below 0.03 mg/L; EBR2 was unaffected by temperature or nutrient stress. Nitrate removal is an important and necessary step for any anaerobic biotreatment process prior to metals reduction; nitrates are reduced under higher ORP conditions and compete with metals for the available electrons. ​​

RO Concentrate: EBR Denitrification Case Study

Comparative parallel batch laboratory tests using an EBR and a conventional fixed bed bioreactor (CBR) were conducted on a mining Reverse Osmosis (RO) concentrate stream (brine) for removal of nitrate-N, cyanide, thiocyanate, and various metal contaminants. The (RO) concentrate streams are a major challenge in the mining industry, as many metals and inorganic species (e.g., Fe, Ni, Se, Zn, NO3-N, NO2-N, total cyanide, cyanate, thiocyanate, etc.) are concentrated in the RO brine stream and require further treatment or disposal. 
​At room temperature, the EBR system achieved nearly 100% nitrate-N removal within one hour (from about 550 mg/L NO3-N in the influent). Under the same testing conditions, only 64% of NO3-N was removed in a CBR. Nitrite-N was completely removed by the EBR system within the first hour of treatment, while only 26% of NO2-N was removed by the CBR in two hours of treatment. 
At 5-8ºC, temperatures, often experienced at mine sites, 94% and 67% of NO3-N removals were achieved with the EBR and CBR, respectively. Additionally, numerous metals, including toxic heavy metals, were removed (i.e., Au, Ca, Co, Cr, Cu, Fe, N, Ni, Pb, Se, Tl, and Zn), with the EBR system showing significantly faster removal kinetics and higher removal efficiency of Cu, Mo, Ni, Se, and Zn. 
​Moreover, total cyanide and cyanate were removed by the EBR treatment to below the detection level of 0.01 mg/L within the first hour of treatment, while thiocyanate was removed by 83% to 3.3 mg/L after two hours of EBR treatment; total cyanide was not effectively treated in the CBR.

Full-Scale EBR Denitrification

Based on the significant improvements in the removal kinetics proven during the pilot-scale trials, Inotec converted an existing Conventional Bioreactor facility into an EBR system. The EBR facility is located at a closed gold mine and operates at flow rates between 100 and 250 gpm.
Conversion began in 2014. Since then, nitrate/nitrite has been reduced by the EBR system from an average of 206 mg/L, as N, to 10 mg/L, as N. In Fall 2016, the system experienced an upset associated with a combination of upstream chemistry changes. Appropriate system adjustments are planned for 2018.

FGD Waters: EBR Denitrification Case Studies

The EBR technology has been successfully evaluated for denitrification with numerous coal-fired power plant FGD waters. EBR denitrification results from two on-site pilot-scale tests presented here demonstrate variability in influent nitrate concentrations. Average nitrate-N concentrations were 17.7 mg/L and 12.0 mg/L for sites A and B, respectively, but varied between 11.6-27.2 mg/L for site A and 4.5-25.0 mg/L for site B. The EBR system in both cases successfully reduced nitrate-N to below the detection limit of 0.1 mg/L.

EBR Case Studies

It's not only Selenium!

The EBR technology is well suited for removal of variety of oxyanions, such as nitrates, sulfates, and dissolved metals.