CICEET Progress Report for the period 9/16/05 Through 3/15/06

Project Title: Integrated Biofilm Reactor for Nitrogen Removal from Wastewater
Principal Investigator(s): Robert Nerenberg
Project Start Date: 9/01/05 (funded as of 11/20/05)

Figures

Figure 1

Figure 2

Tables

Table 1

Tasks to meet objectives
Task 2 ­ Construct Bench-Scale Systems
Task 3 ­ Develop Analytical Methods
Task 4 ­ Continuous Literature Review
Task 5 ­ Performance Screening Tests

Progress on Tasks
Task 2 ­ Construct Bench-Scale Systems. We built a prototype MBfP, simulating an activated sludge (AS) tank retrofitted with a bank of hollow-fiber membranes. We used hydrophobic, microporous membranes manufactured by Mitsubishi Rayon (HFM200TL, Mitsubishi Rayon, Japan). The membranes are made from microporous polyethylene, which encapsulates a dense, polyurethane core. The membrane outside diameter is 280 _m. To prevent entrapment of AS flocs, we provided 1-mm spacings between individual membranes and approximately 1 cm between rows of membranes. Figure 1 (see “Figure 1 for Progress Report 1.gif”) provides a schematic of the MBfP. The MBfP included an aeration tank, a settler, and a solids recirculation system. The aeration tank volume was 3.25 liters, resulting in a hydraulic retention time (HRT) of 6 hours. The total membrane surface area in the aeration tank was 1300 cm². A 5-day SRT was maintained in the system. The settler volume was 5 liters, resulting in a combined HRT of 15 hours. The tank was mixed with a 2-inch magnetic stir bar. The membranes were pressurized with compressed air (20% O2) at 10 psig.

Task 3 ­ Develop Analytical Methods. We developed analytical methods for COD, DO, pH, NO₃^-, NO₂^-, NH₄⁺, and SO₄^2-, and are developing microelectrode techniques for measuring gradients of oxygen, nitrate, nitrite, and ammonia in our biofilms. We purchased a micromanipulator, picoammeter, voltmeter, and Clark type oxygen microelectrodes for the microelectrode analyses. Liquid ion exchange (LIX) microelectrodes are needed for our other microelectrode analytes and, since LIX microelectrodes are not commercially available, we are developing methods to construct them at Notre Dame. Techniques and protocols for fluorescence in situ hybridization (FISH) for study of the biofilm ecology were tested on suspended cultures of denitrifying and nitrifying bacteria.

Task 4 ­ Continuous Literature Review. We compiled and reviewed literature related to our research topic, and this information is being added to a literature review section that will be submitted with our final report.

Task 5 ­ Performance Screening Tests. The MBfP was operated under three loading conditions. The first included an influent of 20 mg/L NH₃-N and no BOD, used to establish a nitrifying biofilm. The second contained 20 mg/L NH₃-N and 120 mgBOD/L of acetate. The third contained 10 mg/L NH3-N and 130 mgBOD /L acetate (see “Tables for Progress Report 1.doc”). Initial reactor results can be seen in Figure 2 (see “Figure 2 for Progress Report 1.GIF”). Our results confirm that the MBfP can achieve concurrent nitrification and denitrification using BOD as an electron donor, with short SRTs. Screening tests are ongoing.

Difficulties
The stir bar at the bottom of the AS tank was not able to provide adequate mixing throughout the tank. As a result, AS flocs settled on the membranes, leading to increased mass transfer resistance. To improve mixing and prevent floc settling, an impellor was added to the side of the tank, and aerators were added to the bottom. The impellor was run continuously, while the aerators intermittently bubbled nitrogen gas. This setup effectively prevented floc settling.

Development of the microelectrode techniques has taken more time than initially anticipated. However, this has not caused delays in other tasks.

Project Objectives for Next Reporting Period

Objectives
The objectives for the next reporting period are: (1) continue bench scale screening tests to determine an effective fiber configuration and mixing approach, and to determine necessary operational parameters; (2) investigate the MBfP biofilm’s microbial function and structure; and (3) begin design and construction of the pilot scale MBfP reactor.

Tasks to Meet Objectives
A second MBfP reactor has been constructed and is currently being operated. We also will develop a simplified setup to explore the biofilm structure and function. Periodic nitrogen gas sparging is being tested as a method to control settling of suspended solids on the membrane bank. Development of microelectrode and FISH techniques is continuing.

Work Plan for Next Reporting Period
Bench scale work will continue at the University of Notre Dame. Design and construction of the pilot scale reactor will begin as a joint effort between APT, Metcalf & Eddy, and the University of Notre Dame.

Anticipated Success in Meeting Project Objectives
No difficulties in completing the project objectives are currently perceived.

Overall Project Timeline Update
The project is currently on track within the proposed schedule.

Preliminary Data
Please see Figures 1 and 2, as referenced above.

Dissemination
Publications: None
Workshops: None
Conferences: “Concurrent Nitrification, Denitrification, and BOD Removal in a Hybrid Membrane Biofilm Reactor” was accepted for platform presentation at the IWA World Water Congress in Beijing, September 2006. Abstracts have been submitted to WEFTEC 2006 and the IWA Biofilms VI Conference 2006, and are under review.
Manuals, Protocols: None
Outreach Activities: None
Contact with End Users: None, other than for End User Report
Patent, Copyright, Invention Disclosure Activity: IP Disclosure submitted to ND Technology Transfer Office for MBfP.

Expenditures
Expenditures were in the range anticipated for the work accomplished to date.

End User Advisor Feedback
Name: Arthur Umble, Ph.D., P.E., D.E.E.
Organization: CDM
Location: Indianapolis, IN
Phone number: (317) 581-9585
E-mail: umbleak@cdm.com

1. At this stage, what are the potential applications for this research? Please discuss how you and others could potentially use the technology.
The obvious application for this technology is addressing near-future Water Quality Based Effluent Limits (WQBELs) in municipal National Pollutant Discharge Elimination System (NPDES) permits for total nitrogen. (This is especially relevant in today’s difficult fiscal environment where most public utilities face significant deficiencies in capital.) Most AS plants in operation today were not designed for total nitrogen removal, yet were designed under 10-State Standards which provide a significant amount of “over-design” paving the way for relatively “simple” membrane-type retrofits of the existing infrastructure. However, as the researchers have already discovered, maintaining sufficient mixing conditions in the reactor when membranes are present may be a challenge in a retrofit application.

This technology should be especially applicable (and attractive) to large industrial indirect dischargers (such as the pharmaceutical, food and paper industries) who are seeking ways to reduce high surcharge fees to their local municipal WWTP.

2. What, if anything, has changed about this project's potential applicability since the last reporting period (not applicable to the first Progress Report)?
Not applicable, as this is the first Progress Report

3. Do you see any key challenges that the researchers may want to address or keep in mind?
From the perspective of settling of biomass, it would be helpful to identify the correlations between sludge volume index (SVI) and the SRT in the various tests. One of the major challenges operators face in full scale operations in conventional AS plants is solids inventories and balance. A common constraint is return activated sludge (RAS) systems being limited in their ability to return “older” more dense sludges within rates that set the basis for design. (For example, a conventional plant may be designed for a return ratio of 0.6 for normal operations. But denser sludges make this difficult because lines can plug. As a result, RAS ratios are set to 1.0 or greater to keep the system moving.) This higher-than-normal return impacts the HRT of the aeration system significantly, thereby reducing overall reaction times, especially for slower reacting nitrifiers. Though this research accelerates the TN removal by sustaining relatively short SRTs, the issue of maintaining a removal efficiencies with decreasing HRTs in the reactor (shorter reaction periods) might need consideration when it comes to full-scale testing.

Another issue that WWTPs are facing more and more with each permitting cycle is the plant’s requirement to fully treat greater and greater peak hydraulic loadings. This is especially true in combined sewer overflow (CSO) communities, but is also true for many communities who must deal with high peaking factors in separate systems due to high infiltration/inflow (I/I). With the presence of membranes, would it not be the case that much greater resistance to flow through the reactor would be experienced? Consequently, would the presence of the membrane units force the operator to “by-pass” more of the primary effluent around the reactor during peak conditions? If this is so, this would create significant regulatory constraints because of the stringent and very complex regulations related to “by-passed” flow volumes. (The high costs, and large land area requirements, associated with adding equalization (EQ) basins to handle high peak wet weather flows limits the options available to treatment facility managers).

Finally, though it may seem intuitively obvious that the biomass should be more “robust” from this technology, the researchers may also want to investigate how, if at all, this process alters the digestibility of the waste sludge (either aerobically or anaerobically) in the solids handling portion of the treatment plant. For instance, how are the volatile contents altered? Are the organisms more robust in the digestion environment?

4. Does this report offer you enough information to adequately address the above questions?
Yes it does.

5. Other feedback?
I’m curious if the hybrid membrane reactor system can be subjected to intentional alternating oxidative environments. For instance, are there any benefits to having portions of the reactor’s plug flow receive no oxygen input thereby generating true anaerobic, or at least anoxic conditions? (Figure 2 indicates this did occur in the latter durations of the test). The thought here is in terms of full-scale operations in potential additional savings to the utility through reductions in energy consumption