1. Page 1 of 22
Treatment of High Strength Acidic Wastewater Without pH Adjustment to Meeting
Secondary Discharge Regulations
Krishna M. Lamichhane, William K. Lewis, Julia J. Wang, Kexin Rong, and Michael J.
Cooney
. Hawaii Natural Energy Institute, University of Hawaii at Manoa, 1680 East West
Road, POST 109, Honolulu, HI 96822.

Corresponding Author, Associate Researcher, E-mail: mcooney@hawaii.edu, Phone: +1 808
956 7337
Abstract
Keywords: Wastewater treatment, packed bed reactor, biochar media, natural pH adjustment,
biogas production, Trickling filter, hybrid filters, discharge regulations
1. INTRODUCTION
Biological processes can be a cost effective wastewater treatment technology in terms of energy
consumption and chemical usage [1]. Conventional wastewater treatment techniques, however,
employ energy intensive aerated systems whose long-term sustainability, both in economic and
environmental impact, are being questioned [2]. Long term sustainability will require the
development of low–energy low-chemical usage treatment technologies that treat wastewater at
high rates. Anaerobic processes are preferred over aerobic processes while treating high strength
(industrial) wastewaters because of its low energy requirements, low sludge production per unit
pollutant (like COD) removal, and biogas production potential. Wastewaters with skewed
nutrient ratio and extreme pH conditions need pre-conditioning before treating in biological
systems. High strength wastewaters such as those separated from grease trap waste or food
processing plants can be highly acidic owing to high concentrations of volatile organic acids[3].
When processing high strength acidic wastewaters, significant amounts of alkali (e.g. sodium
hydroxide, NaOH) must be added in order to raise the pH to levels that support methanogenic

2. Page 2 of 22
microbial communities, maximize biogas production, and prevent sour reactors [3-5]. Base
addition is problematic in application, particularly for small to medium size businesses, as it is
realized through the metered addition of alkali stored in concentrated reservoirs that are highly
regulated and require strict safety training for all personnel involved. The use of alkali chemicals
also creates additional cost burdens and poses problems (for e.g. excess Na) for effluent reuse in
crop irrigation. The development of methodologies for pH control that dramatically reduce, if
not eliminate, the need for alkali addition would be of great benefit.
The effluent from anaerobic treatment processes, however, cannot meet secondary discharge
regulations and, thus, has to be aerobically treated if the purpose of treatment is to also meeting
secondary discharge regulations. Among aerobic systems, trickling filter (TF) is considered a
low-energy low-chemical consuming treatment process which can consistently produce quality
effluents that meet discharge regulations in BOD5 and TSS and the effluent is also nitrified [6].
The TF performance is heavily dependent upon the characteristics of the media (biofilm carrier)
used. Traditionally, the primary selection criteria for TF media have been high surface area per
unit volume and porosity to provide ventilation and minimize clogging [7]. Less attention,
however, has been paid to the quality of biofilms supported by the media. Typical TF media
employed has included beds of rock, slag, or plastic molds [8]. Rock beds are limited by low
surface to volume and void ratios (≤50%), impacts that promote clogging at elevated hydraulic
and organic loading rates. By contrast, plastic media are gaining acceptance because of their high
void ratio (≥ 90%) and high surface to volume (≥100 m2
m-3
) ratios which enhance oxygen
transfer and biofilm thickness control, thus facilitating higher hydraulic and organic (HLR and
OLR, respectively) loading rates [9]. Despite this advance, however, adequate nitrification (75-
85%) and effluent levels of BOD5 and TSS below EPA regulations (<30 mg l-1
) cannot be
expected when treating municipal wastewaters using TF with OLRs greater than 0.29 kg BOD
m-3
d-1
(NESC, 1998) [6]. To meet these demands alternative packing materials are needed.
Various forms of carbon (charcoal, biochar, activated and granulated carbon etc.) have been
used for water purification purposes. Biochar, for example, has been used to treat storm [10] and
grey water [11], to filter drinking water [12], and as a packing material for packed bed anaerobic
reactors treating high strength acidic wastewater [13]. However, despite these positive results
their remains no reports of biochar used as a media in trickling filters.

3. Page 3 of 22
In this work, we report on a methodology capable of processing high strength acidic wastewater
anaerobically with biogas production approaching theoretical limit without the need for alkali
addition (or pH adjustment) and also present data that evaluate the performance of biochar as a
biofilm support media in TF column reactors treating anaerobically treated wastewater streams
possessing organic strengths as high as ~1,800 mg COD per liter. The effluent from the TF is
further processed through a follow-on biochar packed filter – clarifier (BF-clarification) unit to
produce a final effluent that is well below EPA discharge regulations in both TSS and BOD5 and
completely nitrified.
2. MATERIALS AND METHODS
2.1 Experimental set-up
The system consisted of a 16 L capacity feed tank followed by anaerobic and aerobic reactors in
series. The feed tank temperature was maintained at 12˚C by pumping chilled water (ThermoTek
Ink, USA) through heat exchange tubes. The feed was pumped to the hydrolysis tank and the
hydrolyzed water, then, flowed down to anaerobic and aerobic reactors sequentially by gravity.
2.1.1 Anaerobic system: The anaerobic system consisted of a 3L-hydrolysis (HYD) reactor
(effective volume 2L) and a 5L-upflow packed bed column reactor (effective volume 4 L)
connected in series (Figure 1). The HYD reactor and packed bed column reactors were both
made of plastic with inner diameter of 6" and 5.5" (" inch, 1"~2.54 cm), respectively. The
volume of the anaerobic system (volume of HYD reactor, packed bed column, and connecting
pipes combined) was 6.14 L. The temperature of HYD reactor was maintained at 37.5±1.0˚C
through the use of a cartridge heater controlled by an external controller (B. Braun Biotech
International, Micro DCU Twin). The pH of the HYD reactor was monitored with a pH probe
(Mettler Toledo, DPAS-SC K85/225) connected to the same external controller used for the
cartridge heater. A plastic basket of approximately 1.35 L containing 478 grams of wood char
(biocarrier) was inserted in to the anaerobic column. The 8" tall and 3.6" in diameter basket
(cross-section area ~66.58 cm2
) was fabricated from bendable plastic coated wire mesh of
opening approximately 6 mm x 6 mm (Stretchable molded polyethylene, McMASTER-CARR,

4. Page 4 of 22
USA). The temperature of the column was maintained at 37.5±1.0˚C by the use of regulated
heating tape wrapped around the outer wall of the column. Headspace gas produced in HYD and
packed bed reactors left the system through vent pipes fixed in the lids of both reactors. To
ensure external air did not contaminate the head space gas, the gas line leaving the reactor was
passed through a water trap which provided less than 2 mm of head pressure.
Individual recycle lines were installed for mixing within the HYD and packed bed reactors.
Mixing in the HYD reactor was achieved through the use of a continuous recycle loop that
pumped (Eheim pump, type 1046 319, Germany) the reactor liquid through a bottom port and
returned it through a top port (Figure 1). In a similar fashion, mixing in the packed bed reactor
was achieved by a continuous recycle that withdrew fluid through a top port and returned it to
the transfer inlet line to the reactor (Figure 1). The intermittent recycle from packed bed
anaerobic column reactor to the HYD reactor was achieved by withdrawing fluid from the
bottom of the anaerobic packed bed reactor and returning it to the top of HYD reactor (Figure 1).
2.1.2 Aerobic system: The aerobic system, which followed anaerobic system, consisted of a TF
column (5L capacity) and biochar filter (BF)-clarification unit in series, thus, received effluent
from the preceding anaerobic treatment process. The plastic-made 5.5" diameter TF column
reactor used 74.2 grams of biochar (biocarrier) confined in a cylindrical basket of height 10",
diameter 3.6", cross section of 66.58 cm2
, and volume of approximately 1.691 L (Figure 1, a).
The basket was fabricated from bendable plastic coated wire mesh of opening approximately 7.5
mm x 7.5 mm (Stretchable molded polyethylene, McMASTER-CARR, USA).The biochar used
was corn cob char (density 106.7 g/L ± 8.3 g/L) loosely packed in seven layers (~10.6 g per
layer) possessing a void ratio of approximately 50% within the basket. The bottom portion of the
column reactor was tapered inward to form a conical shape that permitted the accumulation of
solids that were removed periodically. The temperature of the TF column was maintained
between 30°-32° C by the use of regulated heating tape wrapped around the outer wall of the
column. Aeration to the column was provided through the insertion of an extruded acrylic tube of
8 mm diameter through the center of the basket. The bottom of the tube was sealed and a number
of small holes drilled into the bottom 1/3rd
portion of the tube. Pressured air was then delivered
via a top inlet port using an external aquarium air pump (Penn-Plax, Silent air X4). Effluent

5. Page 5 of 22
accumulated at the bottom of the column was recycled back to the top of the column and allowed
to trickle down at a recirculation ratio (R) ~ 30, much higher than used in commercial TFs, to
ensure complete media wetting. The TF column was also equipped with an external air lift
system which provided additional oxygenation to water that was either exited to the biochar filter
or recycled to the top of the TF column (Figure 1).
The effluent from the TF was passed to a shallow biochar packed filter (BF) – clarifier system
(Figure 1, b) that further treated the wastewater until collected in a downstream reservoir, final
treated water holding tank, of approximately 82 liters (Figure 1, c). The BF was made of a 5.5"
diameter and 8" high cylindrical plastic container filled with approximately 2.0 cm thick wood
char bed at the bottom overlain by a loosely packed coconut char layer of approximately 8.5 cm.
The coconut char bed was further covered by a thin layer (~0.5 cm) of wood char of relatively
small size (~0.40 mm x 0.40 mm mesh size) giving a total filter depth of approximately 11 cm.
Each layer of biochar was separated by a 0.38 x 0.38 mm wire screen (Stretchable molded
polyethylene 7x7 mesh, McMASTER-CARR, USA). The effluent from the biochar filter flowed
to a downstream clarifier of approximately 7.5 L where it enters at the bottom and slowly rises
and flows over an internal wall and a final brush filter into a treated water holding tank. Clarifier
water is recycled back to the top of the biochar filter through a small submersed pump (EHEIM
645 E, Germany).
2.2 Feed stock: The feed stock used in the anaerobic system was grease trap waste (GTW)
wastewater. The GTW wastewater was obtained from Pacific Biodiesel in Honolulu which
collects GTW from restaurants and food service establishments and separates the wastewater
from fat, oil, and grease (FOG) which is used as feed stock for biodiesel production [14].
Analysis of the GTW wastewater revealed a chemical oxygen demand (COD), total suspended
solids (TSS), total nitrogen (TN), total phosphorus (TP), total volatile organic acids (TVOAs),
hexane extractable materials (HEM) and pH of 19.78 g L-1
, 1.16 g L-1
, 0.51 g L-1
, 0.32 g L-1
, 5.42
g L-1
, 3.93 g L-1
, and 4.0 g L-1
, respectively. The feed was collected in bulk and stored frozen in
10 L containers at -20˚C until used. The aerobic system, as explained before, received the
effluent from the preceding anaerobic system. The anaerobically treated effluent (or the feed
wastewater to TF) possessed an average COD, TN, TP, and TSS concentration of 1,800 mg l-1
,

6. Page 6 of 22
360 mg l-1
, 280 mg l-1
, and 344 mg l-1
, respectively, and comprised largely of small organic acids
and alcohols.
2.3 Sampling: All reactors (HYD, packed bed anaerobic, and TF) were equipped with sampling
ports at different heights. Samples from HYD reactor were collected from a port from above the
conical bottom of the HYD and also from liquid transfer line to packed bed anaerobic reactor.
Samples from the anaerobic column reactor was collected from the effluent exit line and samples
from trickling filter (TF) column were collected from the sampling port at the bottom above the
conical portion of the reactor column. Effluent samples from the biochar filter were collected
from the clarifier.
2.4 Analytical: All collected samples were analyzed immediately for BOD5 (within 1 hour of
collection). Tests for COD, TN, TP, TSS, and ions were executed on the same day of sample
collection to ensure sample consistency. Samples were vigorously mixed prior to analysis of
COD, TN, TP and TSS. Samples were filtered through 1.5 µm filter to determine soluble part of
COD, TN, and TP and through 0.22 µm filter for ion analysis. Measurements of COD, TN, TP,
TSS, and TVOAs were made according to HACH Methods 8000 (HR+), 10072 (HR), 8190, and
8196 for COD, TN, TP, and TVOA, respectively, using kit numbers 24159-25, 27141-00, 27426-
45, and 22447-00, respectively [14]. Accuracy of all testing was confirmed with standards
22539-29, 24065-49, 2569-49, and 14270-10 for COD, TN, TP, and TVOA, respectively. TSS
was measured according to Standard Methods 2540 D. pH was measured using external pH
probe (Denver Instruments, model 250). Ions of environmental significance including
ammonium, nitrate, sodium, and chloride were measured using ion chromatography as per
established methods (Dionex ICS-1100 conductivity detector, Fisher Scientific) in the Water
Resources Research Center (WRRC) lab. Headspace gas production rate was measured through
vent pipes leaving both reactors of the anaerobic system (HYD and packed bed reactor) using
soap bubble columns. The head space gas composition was measured using 2-column GC
(Agilent Technologies 6890) as per protocols previously developed [15]. The base consumption
was measured by measuring the difference in weight of the base dosing container. Major
components of TVOA were also measured by HPLC (Agilent Technologies, Biorad Aminex
HPX-87H column) with a refractive index detector.

7. Page 7 of 22
2.5 System start-up and operation
2.5.1 Anaerobic system: In order to accelerate microbial acclimatization, both HYD and
anaerobic column reactors were inoculated with 500 ml of anaerobically digested sludge
collected from a local wastewater treatment plant (East Honolulu WWTP, Hawaii American
Water). Immediately after inoculation, a low strength feed (three times diluted GTW wastewater,
COD ~6.6 g/L) was fed into the hydrolysis reactor at a 10 day hydraulic retention time (HRT).
During this start-up time, the pH of the hydrolysis reactor was maintained at 5.75 to favor initial
development of the acido and acetogens by the controlled addition of base, 2 M sodium
hydroxide (NaOH), and the base dosing pump controlled by the external controller (B. Braun
Biotech International, Micro DCU Twin). As time progressed, the concentration of the feed stock
solution was increased to full strength GTW wastewater (COD 19.78 g/L) delivered at 7.5 day
HRT. The addition of feed was not continuous, rather it was metered (PULSAtron metering
pump, Pulsafeeder USA) into the hydrolysis reactor for one minute every hour at a rate necessary
to achieve the desired system HRT. The hydrolyzed water, then, flowed down by gravity to
packed bed anaerobic column reactor for further processing. Moreover, fluid from the bottom of
the anaerobic column reactor was continuously recycled back to the hydrolysis reactor for twenty
minutes every hour just prior to the initiation of the pulsed feed. This timing allowed the
recycled hydroxyl ions from the packed bed anaerobic column reactor to raise the pH in the
hydrolysis reactor prior to the addition of the acidic feed. The system was operated continuously
in this way for over five months with the pH setpoint raised intermittently, as shown in Figure 2,
after steady state operation had been reached. Steady state was assumed to have been reached
when reactor performance was stable over a time period in terms of COD, TVOA, and TSS
removal and when base addition was consistent.
2.5.2 Aerobic system: The TF was inoculated with 100 ml of activated sludge collected from the
same wastewater treatment plant (East Honolulu WWTP). The inlet wastewater was fed at a rate
of 0.816 l d-1
thus yielding an organic load of approximately 1.469 g COD d-1
and a specific
OLR of approximately 0.87 kg COD m-3
d-1
. The feed was added in hourly increments required to
achieve the desired averaged hourly flow rate using a metering pump (PULSAtron, Pulsafeeder

8. Page 8 of 22
USA). The continuous air supply to the column TF was delivered at a rate required to maintain a
dissolved oxygen (DO) concentration in the recycle water at or above 3.5 mg l-1
. Steady state
was assumed to have been reached when reactor performance was stable over a time period in
terms of COD removal.
3. RESULTS AND DISCUSSIONS
In this study we report a methodology we developed to anaerobically process high strength
acidic wastewater without the need for external pH adjustment (i.e. base addition) and the low-
energy low-chemical aerobic biological treatment that is capable of treating anaerobically treated
effluent of relatively high strength (COD~1,800 mg/l) to meeting secondary discharge
regulations. The effluent of this combined anaerobic and aerobic system is also highly nitrified.
3.1 Anaerobic system
3.1.1 pH control: Over a period of approximately seventy eight days, the system pH was
incrementally increased until it stabilized at or just above 6.6 without further need for base
addition (Figure 2). The proposed approach of combination of intermittent feeding coupled with
timed system recycle was verified to be an effective method for passive pH control that does not
require addition of base during anaerobic digestion of high strength acidic wastewater. The
technique makes use of free hydroxyl ions produced in the packed bed anaerobic column to
stabilize the pH. At this point, the recycled hydroxyl ions which had been made available owing
to the digestion of volatile organic acids, balanced out the addition of new protons from the
acidic feed media that dramatically reduces/eliminates the need for base addition. Given that the
feed pH was nearly 4.0, the recycled reactor fluid (pH ≥ 6.6) returned nearly 2.5 orders of
magnitude more hydroxyl ions than were present in the added feed, which was sufficient to raise
the pH to the desired setpoint. Support of this theory can be found in the concentration of all
volatile organic acids in the effluent relative to their concentration in the feed (Table 1). With the
exception of acetate, which was also present at very low concentration, all volatile organic acids
were completely degraded. By the end of the experimental period the recycle process had
become so efficient that the system ultimately reached a steady state wherein the hydroxyl ions
initially added as NaOH to neutralize the volatile organic acids present in the feed were being
recycled back to the hydrolysis reactor and thus negating the need for additional external base

9. Page 9 of 22
addition. The process became so effective that by the end of the experiment the pH had steadily
rose to approximately 6.76 which highly favored system performance.
3.1.2 Steady state performance (organics removal and biogas production)
The COD of the final effluent was gradually reduced from 19.78 g L-1
to an average of 1.8 g L-1
after 3 months, yielding a COD reduction of approximately 91% across the anaerobic treatment
process. Concomitantly, a sharp reduction in TVOAs concentration was also achieved (Table 1),
with lactate, formate, butyrate, ethanol, and butyraldehyde completely degraded while acetate
and acetoin remained present in trace concentrations. The mean reduction in TSS was
approximately 72% (mean TSS concentration 0.32±0.19 g L-1
), and TN and TP reduction was
approximately 52% and 29%, respectively. The head space methane gas composition reached
above 66% and a gas production rate of 343.5 L kg-1
COD degraded was achieved along with the
full consumption of all liquid phase volatile organic acids. These results suggest efficient
anaerobic digestion in which the majority of carbon was converted to biogas (CO2 and CH4), a
majority of the suspended solids was digested and a large fraction of the nitrogen and protein
components were left untouched.
3.2 Aerobic system
3.2.1 Organics and TSS removal: Figure 2 presents the COD concentration profile across the
biochar packed TF while Figure 3 presents the same for TSS. Steady state was assumed to have
been reached when reactor performance in terms of COD removal was stable over a time period.
Steady state was achieved after 55 days of operation as the COD level plateaued (Figure 2). The
average effluent BOD5 and TSS values were 27.5 mg l-1
, and 26.6 mg l-1
, respectively, indicating
an ability to meet secondary discharge regulations of less than 30 mg l-1
both on BOD5 and TSS.
These results are encouraging given that the OLR, at 0.87 kg COD m-3
d-1
, was significantly
higher than those typically encountered in conventional single stage TFs with partial nitrification
(0.29 kg BOD m-3
d-1
) (NESC, 1998)[6].
3.2.2 Ammonia nitrification: The nitrification of ammonia to nitrate (NO3
-
) was nearly
complete, with conversion levels above 96% achieved within 54 days of reactor operation
(Figure 4). The concentration of ammonium was reduced from ≥ 340 mg l-1
in the influent to less

10. Page 10 of 22
than 16 mg l-1
in the effluent while the average influent concentration of NO3
-
≤ 2.5 mg l-1
was
increased to an average of 1,087 mg l-1
in the TF effluent.
3.2.3 Post processing: As described above, the effluent from the TF was fed to novel biochar
filter – clarifier (BF-clarifier) unit for final polishing. This is in general contrast to conventional
full scale wastewater treatment systems wherein the TF effluent is first settled prior to its
processing with filtration. The BF-clarifier system further improved the effluent quality to a final
effluent TSS concentration of approximately 20.1 mg l-1
without the need for any filter
maintenance and/or cleaning during the entire experimental period of approximately 5 months.
More, ammonia nitrification approached near completion (>98%). This suggests the possibility
of using biochar as filtration media in full scale installations as a replacement to relatively deep
and heavy structures of slow sand filters. While there are reports (see, for example,
Vijayaraghavan et al. 2014[16]) of using hybrid sand filters using activated carbon layer in
between sand media layers to remove dissolved and suspended organics, there are no known
reports of sole biochar hybrid filters in full scale installations. This also opens up the possibility
of using biochar as an economical substitute for activated carbon in hybrid sand filters for
treating water contaminated with organic and inorganic pollutants as the adsorption capacity of
biochar for heavy metals [17] and persistent organic compounds including phenol [18], PhaRs,
and antibiotics [19-21] has been reported to be comparable with the adsorption capacity of
activated carbon.
4. Conclusions
The study with the proposed reactor configuration i.e. anaerobic treatment (hydrolysis and
biochar packed column reactor) followed by aerobic trickling filter (TF), which also used biochar
as the biosupport media, had proved that high strength acidic wastewater like those collected
from grease traps (COD~20 g L-1
, pH~4) and food service establishments can be biologically
treated without the need for any chemical addition (such as base to acidic waters for pH
adjustment). More, the COD reduction only across the anaerobic system was approximately 91%
with total system COD reduction achieving 98.5%. The biogas production (343.5 L kg-1
COD
degraded) approached the theoretical limit with methane sharing more than 66% of the biogas.
The method we used was only the coupled application of dosed feed addition and intermittent

11. Page 11 of 22
recycling of (anaerobically) treated wastewater to maintain favorable reaction conditions. The
ability of the system to adjust pH internally while treating acidic wastewaters biologically to
produce biogas offers large potential benefits at commercial scale. The single stage biochar
packed trickling filter, that received anaerobically treated effluent with a COD of ~1.8 g/l, was
shown to be very effective when treating wastewaters at OLRs (0.87 kg COD m-3
d-1
) much
higher than those typically applied (≤0.3 kg COD m-3
d-1
) to single stage full scale TF
installations. In addition, after the steady state had been achieved, the ammonia oxidation was
consistently above 96%. Although, the void ratio of the biochar filter media ( ~50%) was much
less than the void ratio of plastic media (~95%) used in conventional full scale TFs, clogging
was not realized and the effluent met secondary discharge regulations on BOD5 and TSS despite
the higher OLRs. The reason for enhanced performance on organics removal and nitrification is
proposed to be due to the effectiveness of the biochar in harboring robust and diverse bacterial
community as explained by Forster et al. (2003) [22]. This enhanced performance implies that
TF reactor sizes can be significantly reduced. TFs packed with biochar can also be operated at
much higher OLRs, making wastewater treatment much energy efficient and, thus,
environmentally and economically sustainable. Finally, the capability of the shallow biochar
filter – clarifier unit operation was found to consistently produce effluents with TSS
concentration much lower than secondary discharge requirements and with near complete
nitrification (>98%).
Combine, these results suggest a novel way of treating high strength acidic wastewater
biologically by simply using intermittent feed and periodic recycling of anaerobically treated
effluent to balance out pH naturally and the superiority of biochar media over the conventional
packing materials used in packed bed/fixed film anaerobic reactors and trickling filters (such as
plastic molds, ceramic rings, rags, and rocks) in water/wastewater treatment industry. More,
biochar can also serve as the cheap and sustainable alternative for the filter media, the sand, used
in slow sand filters and the substitute for activated carbon used in hybrid filters for removing
emerging pollutants of concern (EPOC) from water/wastewater.
Acknowledgements

12. Page 12 of 22
The authors wish to acknowledge funding from the Office of Naval Research (N00014-11-1-0391 and
N00014-13-1-0463)
Figure Legends
Figure 1: Experimental set up of high rate anaerobic treatment system. Key: (1) feed storage tank; (2)
hydrolysis reactor, (3) recycle loop for hydrolysis reactor; (4) packed bed reactor; (5) biochar packed bed;
(6) recycle mixing loop for backed bed reactor; (7) recycle loop from packed bed reactor to hydrolysis
reactor; (9) effluent stream.
Figure 1.1: Experimental setup for aerobic treatment system with trickling filter (TF) and
biochar filter (BF)-Clarifier unit: (a) biochar packed trickling filter (TF), (b) biochar packed
shallow filter (BF), and (c) treated effluent (clean water) collection reservoir.
Figure 2: pH profile of the anaerobic system with base consumption over time. Time zero signifies
beginning of intermittent feed and recycle control algorithm.
Figure 3: COD reduction profile across anaerobic treatment (HYD and packed bed column
reactor combined)
Figure 4: COD reduction profile across a biochar packed trickling filter
Figure 5: TSS concentration profile in the biochar packed trickling filter effluent
Figure 6: Ammonia nitrification through a biochar packed trickling filter (NB: the NO3
-
concentration in the graph is reduced 10 times to fit the plot along with NH4+
plot so effluent
NO3
-
values need to be multiplied by 10 to get actual values)

13. Page 13 of 22
Figure 1: Experimental set up of high rate anaerobic treatment system. Key: (1) feed storage tank; (2)
hydrolysis reactor, (3) recycle loop for hydrolysis reactor; (4) packed bed reactor; (5) biochar packed bed;
(6) recycle mixing loop for backed bed reactor; (7) recycle loop from packed bed reactor to hydrolysis
reactor; (9) effluent stream.

14. Page 14 of 22
Legends:
1 Biochar (media) packing in TF 4 TF effluent outlet
2 TF sampling port 5 BF effluent outlet
3 Air lift recycle
Figure 1.1: Experimental setup for aerobic treatment system with trickling filter (TF) and biochar
filter (BF)-Clarifier unit: (a) biochar packed trickling filter (TF), (b) biochar packed shallow
filter (BF), and (c) treated effluent (clean water) collection reservoir.
(c)(b)
Air out
BF Liquid recycle
Feed
Air in
TF Liquid recycle
Air in
(a)
1
4
2
3
5

15. Page 15 of 22
Figure 2: pH profile of the anaerobic system with base consumption over time. Time zero signifies
beginning of intermittent feed and recycle control algorithm.
0
1
2
3
4
5
6
7
8
0 15 30 45 60 75 90 105 120 135
Base addition (g NaOH) pH set point System pH Feed pH

16. Page 16 of 22
Figure 3: COD reduction profile across anaerobic treatment (HYD and packed bed column
reactor combined)
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80
COD(g/L)
Time (d)
Feed AD effluent

17. Page 17 of 22
Figure 4: Organics (COD) reduction profile across a biochar packed trickling filter
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120
COD(g/L)
Time (days)
Influent COD Effluent COD

18. Page 18 of 22
Figure 5: TSS concentration profile in the biochar packed trickling filter effluent
0
100
200
300
400
500
600
700
800
900
1000
0 20 40 60 80 100
Concentration(mg/L)
Time (days)
Influent TSS Effluent TSS

19. Page 19 of 22
Figure 6: Ammonia nitrification through a biochar packed trickling filter (NB: the NO3
-
concentration in the graph is reduced 10 times to fit the plot along with NH4+
plot so effluent
NO3
-
values need to be multiplied by 10 to get the actual value)
0
50
100
150
200
250
300
350
400
450
40 50 60 70 80 90 100 110
NH4(mg/L)
Time (days)
NH4 in AD NH4 in TF NO3 (* 10) in TF NO3 in AD

20. Page 20 of 22
Table 1: Total volatile acid (TVOA) components reduction over time. Data represents one dataset taken at
120 hours after the start of the intermittent feed and recycle control algorithm
TVOA compounds
Feed
concentration (g/L)
Effluent
concentration (g/L)
Reduction (%)
Lactate 2.23 0 100
Formate 0.06 0 100
Acetate 1.68 0.12 93
Acetoin 3.57 0.042 99
Butyrate 0.59 0 100
Ethanol 0.57 0 100
Butyraldehyde 0.63 0 100

21. Page 21 of 22
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Biological treatment processes. 2013: USA. p. 46.
2. Verstraete, W., P. Van de Caveye, and V. Diamantis, Maximum use of resources present in
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