WEF2008 AnMBR paper1

7/21/2019 WEF2008 AnMBR paper1

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Full-Scale Applications of the Anaerobic Membrane Bioreactor

Process for Treatment of Stillage from Alcohol Production in Japan

Shannon Grant1*

, Ian Page2, Masashi Moro

3, and Tetsuya Yamamoto

3

1ADI Systems Inc., 1133 Regent St., Suite 300, Fredericton, NB, Canada E3B 3Z2

2

ADI Systems Inc., 606A Highland Avenue, Austin, Texas, USA 787033Kubota Corporation, Hanshin Office, 1-1-1 Hama, Amagasaki, Hyogo 661-8567, Japan

* To whom correspondence should be addressed. Email: [email protected]

ABSTRACT

Kubota Corporation has six operating full-scale anaerobic membrane bioreactor (AnMBR)

systems and two more under construction in Japan for treatment of stillage from shochu alcohol

production. The operating systems were commissioned from 2006 to 2008. The AnMBR

process has been demonstrated to have numerous process advantages over more conventionaltechnologies, such as superior effluent quality, and ability to handle high concentrations of COD,

TSS, and FOG, while attaining high organic loading rates (10 to 15 kgCOD/m3d).

AnMBR installations typically operate at 55 C, which provides additional benefits of higherbacterial kinetic rates and less sludge production. The flat sheet Kubota membranes ensure no

biomass is lost to the effluent. COD, BOD, TSS, and FOG removals are typically over 98

percent in the AnMBR process. Despite the very high strength of alcohol stillages, the pairing

of the AnMBR with an aerobic MBR (designed for biological nutrient removal), provides a two-stage process that can produce an effluent with less than 10 mg/l TSS and BOD, and very low

total nitrogen (TN) and total phosphorus (TP) concentrations.

KEYWORDS:anaerobic membrane bioreactor, high strength wastewater, biogas, fouling,

effluent quality, Kubota flat-plate membrane cartridges, submerged membrane unit

INTRODUCTION

Kubota Corporation presently has six operating full-scale anaerobic membrane bioreactor

(AnMBR) systems operating in Japan, and another two under construction, for treating stillagewastewaters from alcohol production. These alcohol plants produce food-grade ethanol [shochu

and awamori] from barley, wheat, sweet potato, and rice feed stocks. The first full-scaleinstallation of the AnMBR process by Kubota was completed in 2000 (for treatment of septage

and garbage), and the initial AnMBR for treatment of alcohol distillery stillage was started up in

January 2006. Kubota presently has fourteen full-scale AnMBR installations operating or underconstruction in Japan. The first full-scale AnMBR system in the USA was constructed and

started up by ADI Systems Inc. in 2008 for treatment of a salad dressing and BBQ sauce


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production wastewater (treating a flow of 500 m3/d and COD load of 19,000 kg/d) at Kens

Foods in Marlborough, MA.

The technology is considered to be cutting-edge technology capable of anaerobically treatingchallenging wastewaters of higher organic strength and solids concentrations.It is appropriatefor industrial applications in cases where space is limited, superior effluent quality is desired,

and where wastewater operations including sludge settling and clarification pose a concern.

The Kubota AnMBR process incorporates anaerobic digestion and membrane filtration in oneprocess technology that effectively treats wastewater and produces an anaerobic effluent of

superior quality with virtually negligible suspended solids ( and in many cases without the need

for pre- and post-anaerobic treatment processes) while maximizing biogas production. It

employs the same successful flat-sheet membrane technology used in Kubota aerobic MBRprocesses (which have now been used in over 2500 installations world-wide). The membranes

(with nominal pore size of 0.4 micron) are submerged directly in the anaerobic biomass and

completely block all suspended solids from escaping to the effluent.

Biogas is used instead of air to scour the membrane surface to keep fouling to a minimum. The

biogas is recirculated from the reactors headspace through the diffusers located beneath the

membrane cartridges. This creates a sparging effect that scours the membrane surface andsignificantly reduces the rate of membrane fouling. Periodic cleaning of the membranes

(typically performed every one to three months) is done in situwith dilute citric acid.

The AnMBR process operates at a higher biomass concentration, typically 30,000 50,000 mg/l

and as a result provides conditions favorable for treatment of high strength industrial

wastewaters under higher volumetric loading rates and longer solids retention times whilemaximizing biomass utilization and ensuring stable performance with the ability to retain all the

biomass within the system.

The process incorporates innovative design combined with new technology and proven

techniques to provide numerous process advantages over conventional anaerobic wastewatertreatment processes. Advantages include:

1. A superior quality effluent is produced on a consistent basis. Typically, the AnMBR

effluent quality is sufficient to significantly reduce and sometimes even completelyavoid an aerobic post-treatment stage.

2. High-rate organic loading rates (10 to 15 kg COD/m3d) are achievable; this

minimizes reactor size and footprint of the treatment plant.

3. Suspended solids (TSS) removal is not required ahead of the process. In some cases,

fat/oil/grease (FOG) removal is not required either. This allows TSS and FOG to be


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digested, simplifying the overall system, eliminating primary treatment, increasingbiogas yield, and reducing waste sludge production, handling and disposal, and

associated costs.

4. Waste activated sludge from a downstream aerobic process can be digested in thesystem. This again simplifies the overall process, increases biogas yield, and further

reduces sludge production, handling and disposal, and associated costs.

5. Complete retention of biomass (by use of membranes) in the process provides added

assurance of a consistent high degree of treatment with negligible effluent TSS

concentrations, and superior process stability.

6. Granular sludge is not required, eliminating the need for obtaining granular seed

sludge and maintaining this type of special form of bios in the system.

7. The process can be operated at thermophilic temperature (55 C) which takes

advantage of better solids digestion, higher bacterial rates, higher biogas yield, and

less sludge production, while avoiding the key disadvantage of conventional

anaerobic systemslosing too much biomass to the effluent (which makesconventional processes inherently unstable at thermophilic temperatures).

THE ANMBR PROCESS CONCEPT

The process concept for the AnMBR system is demonstrated in Figure 1. In Japan, the stillage

from alcohol production is typically a whole stillage in that the suspended solids are alsotreated in the AnMBR process if they are anaerobically degradable (such as for rice and sweet

potato). The high non-degradable suspended solids concentration of barley stillage requires thata significant portion of the suspended solids are removed up front in the process using a screwpress without any chemical addition (producing a thin stillage for treatment in the AnMBR).

The process consists of a solubilization tank, methane fermentation tank, and a submerged

membrane tank. Biogas from the methane tank or membrane tank headspace is used for

scouring the membranes. Excess biogas is often used in the factory boiler to displace fossilfuels, which significantly reduces the carbon footprint of the process by reducing the overall

release of greenhouse gasses.


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Figure 1. Overall conceptual diagram of the AnMBR process

Thermophilic Temperature Operation

In the smaller distilleries in Japan, about a third of the biogas is used to make steam to maintain

the AnMBR process at 55 C (thermophilic temperature). In larger distilleries, the stillage oftenleaves the factory at a temperature which is more than warm enough to keep the reactor at 55 C.

Thermophilic temperature operation provides for process advantages of higher bacterial kinetic

rates (reducing the required reactor volume), higher suspended solids digestion, significantlyless waste sludge generation, and superior membrane performance (i.e., higher membrane flux

and less membrane fouling). Despite the obvious process advantages of thermophilic anaerobicdigestion, more conventional anaerobic technologies cannot take advantage of thermophilicoperation because loss of biomass in the effluent from the system makes the system unstable.

This is because biomass generation is significantly lower at thermophilic temperatures.

However, the membranes in the AnMBR process guarantee that the loss of biomass to theeffluent will be negligible, eliminating the concern for process instability.

Ammonia Toxicity

Ammonia toxicity is a potential concern with anaerobic treatment of stillage wastewaters due to

the high concentrations of nitrogen with some feedstocks. Typically, the ammonia-nitrogen

concentration in a thermophilic reactor should be held to less than 3000 mg/l to avoid toxicity.This means that for some feedstocks such as rice and wheat, dilution water must be added to

keep the ammonia-nitrogen concentration less than 3000 mg/l. Since the AnMBR process

volume is determined by volumetric organic loading rate, the addition of dilution water does notimpact on overall system volume like it does for a CSTR-type anaerobic digester which is

typically designed based on hydraulic retention time (HRT) and solids retention time (SRT),

where for a CSTR, HRT = SRT. The membranes in the AnMBR have to increase as the flow

increases (from the addition of dilution water), but the overall system volume is not affected.


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AnMBR Startup

The startup of an AnMBR system is typically accomplished within a few weeks with adequate

seed sludge. Unlike other conventional anaerobic technologies, the loss of biomass during

startup or regular operation is completely avoided since the biomass is trapped by the physical

barrier of the membranes.

INSTALLATION EXAMPLES

H Company Distillery (Awamori-Shochu)

Kubotas first alcohol distillery AnMBR installation was started up in January 2006 for H

Company in Naha, Okinawa. Awamori-shochu is made from rice (a specific form of long grain

rice imported from Thailand). The H Company AnMBR system operates at 55 C and is

designed to treat 15 tonnes/d of stillage. The photo of the H Company AnMBR system isshown in Figure 2 and the process flow diagram is shown in Figure 3.

The methane fermentation reactor has a volumetric organic loading rate of 11 kg COD/m3d.Biogas methane content varies from 63 to 68 percent. A mass balance on COD based on biogas,shows a conversion rate of 84 percent of the influent COD to biogas. A mass balance on TS,

indicates an overall destruction of TS equivalent to 73 percent in the AnMBR system. Overall

COD removal in the AnMBR system based on influent and effluent COD concentrationsaverages above 95 percent.

The total alkalinity (TA) concentration in the AnMBR is about 6000 mg/l (as CaCO3). VFA

concentrations since startup have consistently been less than 700 mg/l. VFA/TA ratio has

typically been less than 0.2, indicating a very stable anaerobic environment.

The TS concentration in the methane tank has generally been stable between 30,000 and 40,000

mg/l.

The AnMBR effluent is further treated and polished in an aerobic MBR system (with Kubotamembranes). This two-stage MBR system allows for exceptional effluent quality in a very

compact process. Effluent limits of 300/300 mg/l for BOD/TSS concentrations are easily met

on a consistent basis as the overall process produces an effluent with less than 10 mg/l BOD andless than 2 mg/l TSS.


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Figure 2. H Company AnMBR system for treating Awamori stillage

Figure 3. Process diagram of the AnMBR process at H Company for treatment of

awamori stillage.


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Table 2 shows the wastewater characteristics of the Awamori stillage, rice washwater (used fordilution), and the final effluent quality limits and actual treated water effluent quality from the H

Company AnMBR and aerobic MBR system.

Table 2: Stillage, effluent limits, and final treated effluent characteristics

Parameter Stillage Rice

Washwater

Effluent

Limits

Treated

EffluentpH 4.2 -- 5.7-8.7 6.5

COD (mg/l) 77,000 -- -- --

BOD (mg/l) -- 2,230 < 300 < 10

TSS (mg/l) -- 2,300 < 300 < 2

TS (mg/l) 50,700 -- -- --

TVS (mg/l) 49,700 -- -- --

TN (mg/l) 3,920 80 -- --

n-Hex (mg/l) -- -- < 30 < 5

Iodine consumption(mg/l)

-- -- < 220 15

Rice washwater is used to dilute the stillage enough to keep ammonia toxicity from being a

problem with treatment of the awamori stillage (which has a TN concentration of 3900 mg/l).

Due to the high alkalinity concentration and strength of stillage wastewaters, the periodiccleaning of the membranes (once every 1 to 3 months) with 10 percent citric acid does not

impact on the methane tank pH. Citric acid is very effective at cleaning the membranes for both

inorganic and organic fouling. Citric acid is consumed by the bacteria in the bulk solution of themethane tank, thus there is no citric acid residual.

Denen-Shuzo Company Shochu Distillery

The Denen-Shuzo company in Satsumasendia City of Kagoshima prefecture treats Shochu

production from both barley and sweet potato. Typically sweet potato is used as the feed stock

from September to January, producing 20 tonnes/d of stillage, and barley is processed fromFebruary to July producing 12 tonnes/d of stillage.

Figure 4 is a photo of the installation and Figure 5 is a process flow diagram of the process. The

AnMBR system was started up in March of 2007. A screw press is used to remove suspended

solids from the raw wastewater when the plant is discharging stillage from barley feed stock;

solids from sweet potato pass into the AnMBR system without removal.

Post-anaerobic treatment is accomplished with an aerobic MBR designed for biological nitrogenremoval. Phosphorus removal occurs in both the anaerobic and aerobic MBR systems, mostly

through chemical precipitation with ferric chloride. The ferric chloride is also used to tie up the

sulfide and lower the hydrogen sulfide in the biogas.


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Figure 4. Photo of installation at Denen Shuzo distillery Shochu facility with

solubilization tank (tall FRP tank on far right at back), methane

fermentation tank (tall FRP tank to the left of solubilization tank), and

membrane tank (elevated rectangular steel tank between the two tall tanks)

of the AN MBR process, with aerobic MBR process for polishing and

nutrient removal (concrete tank in foreground on the left).

Figure 5: Process flow diagram of Denen-Shuzo distillery AnMBR and Aerobic MBR

system


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Yamamoto-Shuzo Brewing Company Shochu Distillery

The Yamamoto-Shuzo Brewing Company Shochu Distillery AnMBR system was started up in

March 2007. This plant is also located near Satsumasendia City of Kagoshima prefecture and

treats sweet potato and barley feed stocks.

Figure 6 is a photo of the AnMBR system and Figure 7 is a process flow diagram of the system.

Figures 8, 9, and 10 demonstrate the operating data of the AnMBR process in terms of influent

flow, biogas flow, COD removal, and pH and TS concentration in the methane reactor. AsFigure 9 demonstrates, the COD conversion to biogas averages 85 percent in the AnMBR

system (98 percent COD removal is attained by comparing influent and effluent COD

concentrations).

Figure 6: Photo of the AnMBR system at Yamamoto-Shuzo Brewing Co. Ltd.


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Figure 7: Process flow diagram of Yamamoto-Shuzo Brewing Co. Ltd. AnMBR

system

Figure 8: Stillage and biogas flow for Yamamoto-Shuzo AnMBR, 2007-08


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Figure 9: Stillage flow and COD removal based on conversion to methane

Figure 10: Methane tank pH and TS concentration

Larger-scale AnMBR Systems for Shochu Distilleries

There are two larger scale AnMBR systems involving three parallel AnMBR treatment train

systems treating 60 tonnes/d of stillage at H and S company distilleries. Both are also located inKagoshima prefecture. Photos of these two systems are shown in Figures 11 and 12.


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Figure 11: Three parallel AnMBR modules for treating Shochu stillage at 60 tonnes/d

(system commissioned in July 2006)

Figure 12: Three unit AnMBR system at Shochu distillery treating 60 tonnes/d stillage

(commissioned in March 2008)


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Typical AnMBR and aerobic MBR influent and effluent characteristics for treatment of

stillage from shochu production

In many cases the AN MBR process is followed by an aerobic MBR, which includes nitrogen

and phosphorus removal. The combination of AN MBR followed by aerobic MBR ensures

optimum performance while minimizing reactor volumes and overall plant footprint.

Table 2 demonstrates the typical wastewater characteristics and AN MBR and aerobic MBReffluent quality from the full-scale installations treating stillage from alcohol production.

Table 2: Typical full-scale raw wastewater (influent) and AN MBR and aerobic MBR

effluent quality characteristics while treating stillage from alcohol

production

Parameter Influent AN MBR Effluent MBR Effluent

pH 3.9 7.4 7.1

COD, mg/l 110,000 2,000 180

BOD, mg/l 79,000 1,500 < 10

TS, mg/l 72,400 3,900 600

TSS, mg/l 25,300 < 10 < 10

TN, mg/l 5,250 1,480 40

FOG, mg/l 1,600 50 < 5

AnMBR APPLICATION TO FUEL-GRADE ETHANOL STILLAGE

Although the stillage applications discussed above are for drinking alcohols, stillage fromcommercial fuel-grade ethanol production is similar in characteristics, particularly if the same

feed stocks are used (wheat, barley, sweet potato, and rice). Corn ethanol is similar but has

higher concentrations of oil and magnesium.

Research and pilot demonstration of the AnMBR process for application of the process to cornstillage from ethanol production indicates that more struvite is formed in the AnMBR system as


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a result of higher magnesium concentrations. The struvite does not significantly impact themembranes in terms of flux or fouling trends. Struvite can build up on the bottom of the

reaction tanks in the form of heavy crystals. Floor piping needs to be placed for removal of the

struvite layer with the waste anaerobic sludge.

Corn oil breaks down readily in the AnMBR process at thermophilic temperatures. However,

the fraction of oil buildup in the sludge needs to be monitored, and organic loading ratescontrolled to prevent the oil from accumulating in the sludge.

CONCLUSIONS

1. There are now five full-scale anaerobic MBR systems in Japan treating stillage fromcommercial grade alcohol production of Shochu from barley, wheat, rice and sweet

potato feed stocks. The initial installation was commissioned in 2006.

2.

Typical COD removal in the AnMBR process is 98 percent, with 85 percent of theinfluent COD being converted to biogas.

3. Overall TSS and BOD removal in the AnMBR process is typically 100 and 98 percent,

respectively. With an aerobic MBR process for treatment of the anaerobic effluent, theoverall BOD removal is virtually 100 percent, with final effluent TSS and BOD

concentrations of less than 10 mg/l possible. Significant nitrogen and phosphorus

removal is also possible with proper design of the aerobic MBR.

4. The AnMBR process for alcohol stillages can use the high temperature of the stillage

discharge to operate at 55 C, a thermophilic temperature. Thermophilic operation takes

advantage of higher bacterial kinetic rates (less reactor volume), significantly less sludgeproduction, higher FOG and TSS digestion, and superior membrane performance (i.e.,

higher membrane flux and less membrane fouling).

5. The AnMBR process loading rate for stillage applications is typically 10 to 15

kgCOD/m3d. This is considered a high-rate loading condition. In many applications the

AnMBR process can handle high influent concentrations of TSS (if most of the TSS isdegradable) and FOG, unlike other high rate anaerobic technologies. This represents

significant savings in primary treatment and operating costs, as well as providing higher

biogas production.

6.

Ammonia toxicity can be a concern when influent TN concentrations are high enough tocreate an ammonia-nitrogen concentration in excess of 3000 mg/l in the anaerobic

system, as is the case with certain stillages, such as from rice and barley feed stocks.Dilution water or waste streams are used to maintain the ammonia concentration less

than 3000 mg/l in the AnMBR process. The AnMBR process volume is not affected by

dilution water; however, more membrane surface area is necessary to accommodate thedilution water flow.


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7. Rapid AnMBR process startup is possible when adequate effective seed sludge is added.Biomass loss from the system is not a concern with the process.

8. Citric acid is typically used to periodically clean the membranes in situ (about once

every one to three months). Stillage wastewaters have more than enough alkalinity suchthat there is no affect on methane tank pH during and after cleaning. The citric acid is

especially effective for removing inorganic foulants. For organic fouling, other

chemicals such as sodium hypochlorite may be more effective.

9. Stillage from fuel-grade ethanol production is also very treatable with the AnMBR

process. Higher concentrations of magnesium and oil from corn stillage need to befactored into the system design, to avoid excessive buildup of struvite and oil.

Documents

WEF2008 AnMBR paper1