A UNIQUE PROCESS
FOR
UPGRADING CONVENTIONAL ACTIVATED SLUDGE SYSTEMS
FOR
NITROGEN REMOVAL
By:
Thomas P. Gilligan
Lotepro Corporation
Dr. Manfred Morper
Linde AG
CWEA 73rd Annual Conference
April 2001
A UNIQUE PROCESS FOR UPGRADING ACTIVATED SLUDGE SYSTEMS
FOR NITROGEN REMOVAL
By Thomas P. Gilligan and Dr. Manfred R. Morper
ABSTRACT
The LINPOR® process is a modified activated sludge system which utilizes a suspended media of highly porous plastic foam cubes that serve as a mobile carrier material for accumulation of activated sludge microorganisms. This porous media allows the biological reactor to operate at 2 to 3 times greater total biomass concentration than a conventional air activated sludge process. In addition, because most of the biomass is retained in the media, the mass loading imposed on the secondary clarifier is minimized.
A LINPOR System is characterized by a biological reactor where 10 – 30% of the liquid volume is occupied by the highly porous plastic foam cubes which provide the large surface area for accumulation of the microorganisms. Fine bubble diffusers are typically used for mixing and oxygen mass transfer. The LINPOR system can be configured according to the level of treatment required (carbonaceous, ammonia removal or total nitrogen removal) and the process is ideally suited for the upgrade of existing systems to increase capacity, or to achieve higher levels of treatment, while minimizing modifications to existing facilities.
This presentation will address the development and evolution of the LINPOR process from initial pilot plant studies, process design concepts, and operation and performance results from full scale facilities. It will also present results from nutrient removal pilot plant studies conducted at a New Jersey wastewater treatment facility. As an increasing number of plant owners and operators face the need for capacity and/or treatment level upgrade, this presentation will provide specific examples of LINPOR process implementation at existing facilities.
KEYWORDS
Activated sludge, biological nutrient removal, attached growth systems, nitrification, denitrification, upgrading of activated sludge systems.
INTRODUCTION
The LINPOR System is an activated sludge process for secondary biological treatment of wastewater which was developed by Linde AG in the mid-1970’s and commercially introduced in Europe during the early 1980’s. The LINPOR System utilizes a suspended porous support media which allows substantially higher biomass concentrations to be effectively maintained in the biological reactor than without such carrier material. The higher total biomass concentration allows higher reactor volumetric loadings at biomass loadings similar to the conventional air activated sludge process, and produces a treated effluent quality equal to or better than the conventional activated sludge process.
Based on extensive laboratory, pilot plant and full scale operations LINPOR Systems have demonstrated the capability to substantially increase the treatment capacity of existing wastewater treatment facilities while solving biomass settleability and effluent quality problems.
A LINPOR-reactor is an aeration tank where typically 10-30% of the volume is occupied by highly porous plastic foam particles that serve as a mobile carrier material for viable microorganisms.
This carrier material, a typical sample of which is shown in Fig. 1, is the critical element of the process. It must comply with very high quality standards with regard to porosity, homogeneity, particle dimension, wetability as well as mechanical, chemical and biological stability.
Another feature of all LINPOR-systems is a specially designed screen, usually made of perforated stainless steel plates, that keeps the biomass carrying foam media inside the bioreactor and prevents their wash out with the effluent flow. Figure 2 shows such a screen in an empty LINPOR-reactor. Air bubble diffusers are provided in front of the effluent screen to prevent clogging by accumulating carrier media.
Air lift pumps are useful to prevent excessive build-up inside the carrier material and improve distribution of carrier material, particularly in long and narrow tanks with high drift, by returning a certain percentage of the carrier material from the rear to the front end of the tank. At start-up the carrier material is fed batchwise into the operating aeration tank. Spreading activated sludge on the initially formed floating layer enhances wetting and biomass growth on the carrier material and makes it submerge and incorporate into the hydraulic regime of the liquid.
PROCESS REQUIREMENTS for BIOLOGICAL NITROGEN REMOVAL
In order to remove nitrogen from wastewater biologically, combined nitrification/denitrification processes are used. Nitrification, i.e. the biological oxidation of ammonium to nitrate, is the crucial step, as it requires specific reaction conditions. The critical design and operating parameter is the sludge retention time (SRT), defined as the quantity of biomass under aeration divided by the quantity of biomass lost daily from the system either in the effluent or waste streams.
SRT = MLSS x V(1)
(WAS x WSS) + (Q x ESS)
In a conventional activated sludge basin the biomass concentration achievable in the system is a function of the recycle sludge concentration and recycle ratio.
MLSS = RSS x R/Q (2)
1 + R/Q
LINPOR®-CN
In a LINPOR-CN reactor substantially higher MLSS levels can be maintained due to the fixed biomass fraction within the carrier media which would comprise fraction H of the aeration volume. Combining equations (1) and (2), and accounting for the fraction of the tank volume associated with the suspended and fixed solids, yields the following;
SRT = {[RSS x R/Q x (1-H)] + [H x MLSSf]} x V (3)
1 + R/Q (WAS x WSS) + (Q x ESS)
The required SRT is dependent on specific environmental parameters including wastewater temperature, dissolved oxygen level, pH and existence of any inhibitory substances. Once converted to nitrate, the nitrogen pollution load is subjected to anoxic conditions in denitrification reactors, where activated sludge bacteria convert the nitrate to gaseous nitrogen, using carbonaceous oxygen demand as a reducing agent. Nitrogen removal activated sludge plants differ from those removing only carbonaceous pollution by having a much lower organic loading in order to maintain the minimum required SRT, and by having additional non-aerated tankage when denitrification is required.
Figure 3 provides a schematic of the LINPOR-CN process. The key feature of the process is the increased biomass concentration under aeration, which provides a higher sludge age in the same aeration volume as in a conventional plant, thus providing nitrification at higher organic loadings.
Fig. 3 – LINPOR-CN Schematic
In addition to the enhanced nitrification, it has been observed in full scale and pilot plant performance, that LINPOR-CN plants also provide simultaneous denitrification, generally between 20% and 50%, without specific anoxic tankage. The reason for this important result is most probably an anoxic environment inside the biomass containing carrier particles, providing countless miniature denitrification reactors.
LINPOR®-N PROCESS
The main application for this version of a LINPOR system is the removal of nitrogen by oxidation to nitrate from waste waters low in organic load, such as secondary clarifier effluents. Under these conditions the LINPOR-N System is basically an add on process which specifically separates the slow growing nitrifers from competition with the fast growing bacteria feeding on carbonaceous material. Utilizing a LINPOR reactor results in having practically the entire slow growing nitrifier biomass fixed on the carrier material. As there is no suspended biomass that can be washed out, clarifiers and sludge recycle systems are not needed with the LINPOR-N system.
Typical design parameters for the LINPOR-CN and LINPOR-N systems are provided in Table 1.
Table 1
Parameter / LINPOR-CN / LINPOR-NRetention Time, / hrs / 4 – 8 / 2 - 6
Temperature, / C / 8+ / 8+
BOD Loading, / lbs/1000 cf-d / 20 – 80 / -
TKN Loading, / lbs/1000 cf-d / 10 – 20 / 10 - 40
lbs/lb MLVSS-d / 0.1 – 0.2 / 0.1 – 0.2
MLSS (total), / Mg/l / 5 – 10,000 / 2 – 5,000
Media Volume, / % / 10 – 30 / 10 - 30
OPERATING PERFORMANCE
Freising, Germany: The Freising sewage treatment plant was the first existing activated sludge plant ever to be converted to a LINPOR-system. This occurred in 1984 and detailed reports on this conversion are available (Hegemann et al. 1986; Morper 1991). Although the conversion was only intended for an improved COD and BOD removal, the higher biomass concentration and associated sludge age increase was so substantial that nitrification, along with good simultaneous denitrification, was achieved and the system actually operated as a LINPOR®-CN system.
With a change in effluent permit limits for continuous nitrogen removal, and considering anticipated pollution load increase due to economic growth spurred by the new Munich airport, another capacity increase was necessary. Because of the limited site available, a conventional expansion by simple addition of extra tank volume was ruled out at an early stage of planning. Based on the positive experience after the first upgrade, the capacity expansion incorporated a LINPOR system and minimized the reactor volume expansion. A denitrification chamber in front of each LINPOR reactor was installed to assure good overall denitrification.
Figure 4 indicates the addition of a new LINPOR-CN reactor (Tank No. 3) and addition of an upstream denitrification chamber to the existing aeration tanks. The construction sequence avoided interruption of plant operation by construction and startup of the new LINPOR-CN reactor prior to shutdown and modification of existing tanks 1 and 2. The 8 year old carrier material was simply pumped over and used in the new reactor.
Denit. Vol, mg
/ Nitr. Vol., mgTank 1 / .0425-.085 / .325-.3675
Tank 2 / .0425-.085 / .325-.3675
Tank 3 / .075-.15 / .5875-.6625
Figure 4 – Freising LINPOR®-CN Expansion
Table 2 provides the design and operating data for the Freising facility and indicates excellent BOD, NH4N and Total N effluent quality. LINPOR-CN reactor suspended and fixed mixed liquor suspended solids was 7,600 mg/l and 18,000 mg/l, respectively.
Table 2
Design
/ May-June 1995Influent
Flow, MGD
/ 5.2 / 6.9BOD, mg/l
/ 222 / 225COD, mg/l
/ 397 / 425TKN, mg/l
/ 46.6 / 28NH4N, mg/l
/ 35.9 / 22NOXN, mg/l
/ 2.6 / 5Total N, mg/l
/ 49.2 / 34Effluent
BOD, mg/l
/ 2COD, mg/l
/ 20TKN, mg/l
/ --NH4N, mg/l
/ <5 / 0.3NOXN, mg/l
/ -- / 7.3Total N, mg/l
/ <18 / 7.4Reactor
MLSS susp., mg/l
/ 3800 / 7600MLSS fixed, mg/l
/ 15,000 / 18,000MLSS total, mg/l (N&DN)
/ 5,800 / 9,680carrier vol., %
/ 22 / 20F/M
/ 0.12 / 0.12Figure 5 presents a photograph of the Freising plant following upgrade.
Figure 5 – The LINPOR®-CN system at Freising/Germany
Unterföhring, Germany: Figure 6 provides a plan view of the Unterföhring facility. The plant was upgraded from carbonaceous removal to nitrification and put into operation in March 1998. The upgrade incorporated conversion of the 1710 m3 tankage into 1200 m3 oxic tankage and 510 m3 anoxic volume. The LINPOR suspended foam media was equivalent to 18 percent of the oxic tank volume. Additional anoxic tankage was necessary to meet the denitrification requirements and an additional 260 m3 volume was obtained from the existing primary clarifier.
Figure 6 Plan view of Unterföhring LINPOR-CN System
Design parameters for the Unterföhring facility are provided in Table 3.
Table 3
Influent
Flow, MGD0.9
BOD, mg/l353
Lbs/day2646
COD,mg/l810
Lbs/day6085
TKN,mg/l85
Lbs/day635
Effluent
BOD, mg/l<20
COD,mg/l<70
N (total), mg/l<10
Reactor
BOD Ldg, lbs/1000 cf62.4
TKN Ldg, Lbs/1000 cf15
Starnberg, Germany: The Starnberg facility is located southwest of Munich, Germany and serves the communities bordering the pristine LakeStarnberg. Due to severe site constraints, facility capacity expansion had to be done within existing tankage. This was accomplished with the LINPOR-CN upgrade (Figure 7 ). The LINPOR media accounts for 22% of the oxic tank volume. The anoxic volume includes a combination of partitioning off from the existing oxic tankage in addition to utilization of two of the four existing primary clarifiers as anoxic denitrification tankage. The upgraded system will be put into service in late 1999.
Figure 7 Plan view of Starnberg LINPOR-CN System
Design parameters for the Starnberg LINPOR-CN system are provided in Table 4.
Table 4
Influent
Flow, MGD6.34
BOD, mg/l250
Lbs/day13,228
COD,mg/l500
Lbs/day26,455
TKN,mg/l2756
Lbs/day52
Effluent
BOD, mg/l<10
COD,mg/l<60
N (total), mg/l<20
Reactor
BOD Ldg, lbs/1000 cf58.5
TKN Ldg, Lbs/1000 cf12.2
Aachen-Eilendorf, Germany: The Aachen-Eilendorf facility is located in northwest Germany and represents a very innovative upgrade approach to increase level of treatment while minimizing new construction. Since the discharge from the Aachen-Eilendorf facility is a significant portion of the receiving stream flow, a very stringent effluent permit level of 1.0 mg/l NH4N was required. The upgrade incorporated the addition of a LINPOR-N system as a tertiary treatment step to the existing secondary treatment facility. The LINPOR-N tankage was constructed within the walls of the existing secondary clarifier as depicted in Figure 8. The existing secondary clarifier diameter was reduced from 54 m to 36 m by installation of an internal wall, and a new parallel clarifier of the same dimension was built. The inner area continued to serve as the secondary clarifier for the existing secondary treatment system, while the outer periphery serves as the LINPOR-N reactor. There is no clarification following the LINPOR-N reactor. The 2300 m3 LINPOR-N reactor was fitted with diffusers and included media equivalent to 22% of the volume.
Figure 8 - Plan view of Aachen-Eilendorf LINPOR-N System
Design data for the Aachen- Eilendorf LINPOR-N system is provided in Table 5.
Table 5Influent
Flow, / MGD / 7.0
TKN, / Mg/l / 10
Lbs/day / 591
Effluent
BOD5, / Mg/l / < 7
NH4N, / Mg/l / < 1
Reactor
TKN Loading, / Lbs/1000cf-d / 7.3
A listing of additional LINPOR nitrification facilities is provided in Table 6.
Table 6
LINPOR Nitrification Plants
Gemeinde Ilmensee / Municipal-CN / 2,000 P.E. / 1987Stadt Wyk auf Fohr / Municipal-N / 22,000 P.E. / 1988
Gemeinde Halblech / Municipal-N / 0.50 MGD / 1989
Hohenlockstedt / Municipal-N / 0.28 MGD / 1989
Port Kembla, AUS / Coke Oven-N / 1.0 MGD / 1991
Stadt Aachen / Municipal-N / 33.0 MGD / 1992
Stadt Heinsberg / Municipal-N / 50,000 P.E. / 1992
Stadt Freising / Municipal-CN/P / 5.1 MGD / 1992
Stadt KÕln-Weiden / Municipal-N / 75,000 P.E. / 1992
Aachen-Eilendorf / Municipal-N / 130,000 P.E. / 1992
Stadt Erkelenz / Municipal-N / 45,000 P.E. / 1993
Gemeinde Hinterstoder, Austria / Municipal-CN / 10,000 P.E. / 1993
HornsbyHeights, AUS / Municipal-CN / 19,000 P.E. / 1993
Walfeucht -Haaren / LINPOR-N / 17,000 P.E. / 1994
Gemeinde Unterföhring / Municipal-CN / 20,000 P.E / 1998
AV Schotten/Nidda / Municipal-CN / 40,000 P.E. / 1998
ZKS Dillingen / Coke Oven-CN / 0.4 MGD / 1998
AV Starnberg / Municipal-CN / 100,000 P.E. / 1999
Stadt Vilsbiburg / Municipal-CN / 17,000 P.E. / 1999
Note: 1.Plant capacity is given in million gallons per day (MGD) or population equivalants (P.E.) if flow is not available.
Edgewater, NJ Pilot Plant
: Figure 9 provides a schematic of the LINPOR Pilot Plant set up at the Edgewater Wastewater Treatment Plant. Noted on the schematic is provision for bypass around the primary and final clarifiers. This was necessary for flexibility to demonstrate both the LINPOR-CN and LINPOR-N processes. For the LINPOR-CN program raw wastewater was settled in a primary clarifier prior to feed to the LINPOR-N reactor and final clarification.
The LINPOR-N demonstration program provided for feed to the LINPOR reactor from the existing full scale facility secondary effluent. Discharge from the LINPOR reactor was direct to the effluent, without final clarification. This is a critical aspect, and advantage, of the LINPOR-N process that since the nitrifier biomass is developed and maintained within the cube media and not in the bulk fluid, there is no need for final clarification. Figure 10 provides a picture of the LINPOR Pilot Plant setup.
Fig. 10 – LINPOR Pilot Plant – Edgewater, N.J.
Table 7 presents the operating and performance data for the LINPOR-CN and LINPOR-N programs.
Table 7 - Edgewater, NJ: LINPOR Pilot Plant Data
Influent
/ LINPOR-CN / LINPOR-NBOD5, / Mg/l / 169 / 22.8
COD, / Mg/l / 406 / -
TSS, / Mg/l / 201 / 18.0
TKN, / Mg/l / 31 / 14.7
NH3-N, / Mg/l / 17.1 / 10.5
NO3-N, / Mg/l / 0.3 / -
Alkalinity, / G/l CaCO3 / 168 / 167
pH, / SU / 6.9 / 6.4
Effluent
BOD5, / Mg/l / 10.7 / 5.4COD, / Mg/l / 62.5 / -
TSS, / Mg/l / 23.2 / 13.8
TKN, / Mg/l / 2.0 / 1.9
NH3-N, / Mg/l / 0.1 / 0.6
NO3-N, / Mg/l / 15.7 / 11.6
Alkalinity, / G/l CaCO3 / 59.4 / 85.3
pH, / SU / 6.8 / -
LINPOR Reactor
Retention Time, / Hrs / 5.4 / 3.2Temperature, / *C / 15-26 / 20-26
BOD Loading, / Lbs/1000 cf-d / 47.7 / 10.6
TKN Loading, / Lbs/1000 cf-d / 8.7 / 7.5
Media Volume, / % / 20 / 20
MLSS, / Mg/l / 7,292 / 5564
SUMMARY
Long term operation of full scale facilities in Europe, and pilot plant operation in the U.S., have confirmed LINPOR System design parameters, demonstrated excellent performance results and confirmed significant benefits of the upgrade of existing activated sludge systems to nitrogen removal through incorporation of the LINPOR suspended media processes.
ABBREVIATIONS USED
ESSmg/leffluent suspended solids
H -fraction of aeration tank occupied by carrier material
MLSSmg/lmixed liquor suspended solids
MLSSfmg/lfixed mixed liquor suspended solids
QMGDinfluent flow
SRTdayssludge retention time
VMGaeration tank volume
WASMGDwaste sludge flow
WSSmg/lsuspended solids concentration of waste sludge flow
REFERENCES
- Kumke, G.W., “LINPOR Systems – An Activated Sludge Process Using Suspended Foam Media.” 1988.
- Morper, M.R., “Upgrading of Activated Sludge Systems for Nitrogen Removal by Application of the LINPOR-CN Process”, 1994.
3.Morper, M.R., “The LINPOR Processes – Experiences from Full Scale Operation”, 1996.
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