IJAMBR 2 (2014) 30-42 ISSN 2053-1818

Performance of a trickling filter for nitrogen and phosphorous removal with synthetic brewery

wastewater in trickling filter biofilm

Haimanot HABTE LEMJI* and Hartmut ECKSTÄDT

Faculty of Agricultural and Environmental Sciences, Institute of Hydromechanics and Water Management, University of Rostock, 18055 Rostock, Germany.

Article History ABSTRACT Received 01 May, 2014 Received in revised form 31

May, 2014 Accepted 06 June, 2014 Key words: Bioreactor, Brewery wastewater, Flow rates, Phosphorous, Nitrogen. Article Type: Full Length Research Article

The aim of this investigation was to confirm a trickling filter filled with gravel as an alternative biological process over conventional high cost treatment process with regard to nutrient reduction from brewery wastewater. Steady state evaluation of the trickling filter aerobic and anaerobic biofilm system for nutrient removal was made. The results obtained reveal that the bioreactor’s average efficiency ranged from 65.46 to 86.59% and from 10.45 to 56.66% for total nitrogen (TN) and total phosphorus (TP), respectively as the flow rates changed from 900 to 1100 Ld

-1 and at influent chemical oxygen demand (COD)

concentration of 1000 mgL-1

. The average influent nitrogen concentration was 36.9 mgL

-1 whereas for total phosphorous it was 30.74 mgL

-1. There exist strong

correlations between mass loading rate and mass removal rate as suggested by linear regression model. There was only slight variation in the performance of the bioreactor as the COD load changes. The trickling filter achieved nitrogen and phosphorous removal efficiencies of 72.10±18.49 and 74.69±14.14 (mean±SD), respectively at the design COD load and flow rate of 1648 mgL

-1 and

1100 Ld-1

. At the steady state biofilm state, the trickling filter achieved a total nitrogen and total phosphorous removal efficiency of 88 and 80%, respectively for average influent nitrogen and phosphorous concentration of nearly 39.63 and 11 mgL

-1. At this steady state biofilm state, the performance for ammonium

removal was about 98% at influent concentration of 22.54 mgL-1

. From these results, it can be concluded that the nutrient load of brewery wastewater can be handled in a cost-effective and environmentally friendly manner using the gravel-filled trickling filter.

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INTRODUCTION Nutrients mainly refer to inorganic matter from runoff, landfills, livestock operations and crop lands. The two primary nutrients of concern are phosphorus and nitrogen (Rob et al., 1992). Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of

*Corresponding author. E-mail: haimanot.lemji@uni-rostock.de. Tel: +4915223895698.

nutrients. In 2011, the United States Environmental Protection Agency (EPA reported that excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns, including eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, nitrogen saturation in forests and global warming (EPA, 2004).

Eutrophication or more precisely hypertrophication is the ecosystem response to the addition of artificial or natural substances such as nitrates and phosphates

through fertilizers or sewage, to an aquatic system (Schindler and Vallentyne, 2004). One example is the "bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. The addition of phosphorus increases algal growth, but not all phosphates actually feed algae (Hochanadel, 2010). These algae assimilate the other necessary nutrients needed for plants and animals. When algae die, they sink to the bottom where they are decomposed and the nutrients contained in organic matter are converted into inorganic form by bacteria. The decomposition process uses oxygen and deprives the deeper waters of oxygen which can kill fish and other organisms.

When an ecosystem experiences an increase in nutrients, primary producers reap the benefits first. In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is required by all aerobically respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off (Horrigan, 2002). In extreme cases, anaerobic conditions ensue; promoting growth of bacteria such as Clostridium botulinum that produces toxins deadly to birds and mammals. Zones where this occurs are known as dead zones.

Some algal blooms, otherwise called "nuisance algae" or "harmful algal blooms", are toxic to plants and animals. The toxic compounds they produce can make their way up the food chain, resulting in animal mortality (Anderson, 1994). Freshwater algal blooms can pose a threat to livestock. When the algae die or are eaten up, neuro- and hepatotoxins are released which can kill animals and may pose a threat to humans (Lawton and Codd, 1991; Martin and Cooke, 1994). An example of algal toxins working their way into humans is the case of shellfish poisoning (Shumway, 1990). Bio toxins created during algal blooms are taken up by shellfish (mussels, oysters), leading to these human foods acquiring the toxicity and poisoning humans. Examples include paralytic, neurotoxic, and diarrhoetic shellfish poisoning. Other marine animals can be vectors for such toxins, as in the case of ciguatera, where it is typically a predator fish that accumulates the toxin and then poisons humans.

Eutrophication may cause competitive release by making abundant a normally limiting nutrient. This process causes shifts in the species composition of ecosystems. For instance, an increase in nitrogen might

Int. J. Appl. Microbiol. Biotechnol. Res. 31 allow new, competitive species to invade and out-compete original inhabitant species.

Eutrophication poses a problem not only to eco-systems, but to humans as well. Reducing eutrophication should be a key concern when considering future policy for everyone, including farmers and ranchers, seems feasible. While eutrophication does pose problems, humans should be aware that natural runoff (which causes algal blooms in the wild) is common in ecosystems and should thus not reverse nutrient concentrations beyond normal levels. Cleanup measures have been mostly, but not completely, successful. Finnish phosphorus removal measures started in the mid-1970s and have targeted rivers and lakes polluted by industrial and municipal discharges. These efforts have had 90% removal efficiency (Räike et al., 2003). Still, some targeted point sources did not show a decrease in runoff despite reduction efforts.

Eutrophication was recognized as a water pollution problem in European and North American lakes and reservoirs in the mid-20

th century (Rodhe, 1969). Since

then, it has become more widespread. Surveys showed that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28% [International Lake Environment Committee (ILEC), 1988–1993].

Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes. The concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Between 1950 and 1995, an estimated 600,000,000 tonnes of phosphorus were applied to Earth's surface, primarily on croplands. Policy changes to control point sources of phosphorus have resulted in rapid control of eutrophication. The World Resources Institute has identified 375 hypoxic coastal zones in the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US and East Asia, particularly Japan (Selman, 2007).

In trickling filters which are packed bed reactors, the effluent flows downward thus trickling on the surface area of the packed bed particles whereas the organic and nutrients are assimilated by the biomass growing on the packed bed media. This is the basic principle underlying the high water treatability of this biological treatment method (Wik, 1999). Trickling filters, trickling bio filters and tower filtration technologies are regarded as well-established treatment technologies for municipal wastewater (Metcalf and Eddy, 1991). Unlike the other conventional treatment technologies, trickling filter do not require high investment in mechanical or energy demanding equipment and does not require much human attendance for operation and maintenance of the

Habte Lemji and Ecktädt 32

A B C

Figure 1. The River stone medium: A, (16-32mm); B, (32-64mm); C, (80-100mm, support). Source: Habte Lemji and Ecktädt, 2014

Table 1. Physicochemical properties of the local brewery effluent on different days of beer production.

COD BOD5 NH4−N NO3−N NO2−N TN PO43- TP T° pH

1650 1144 3.63 0.654 0.586 31.0 8.33 11.64 17 8

3949 3444 8.21 3.23 0.173 55.8 5.63 14.3 31 9

11023 8664 13.8 11.1 0.588 229 38.2 73.2 26 12

1599 1215 3.25 16.9 0.590 44.1 5.88 11.64 26 8

1970 1548 2.77 2.32 0.433 34.1 3.6 9.84 32 9

1345 1100 3.63 0.654 0.586 31.6 8.33 11.64 17 8

9217 4245 2.17 19.6 0.221 128 26.5 38 25 11

4225 3500 4.44 3.19 0.096 58.7 4.55 14.5 34 10

2258 1921 4.83 3.22 0.063 33.9 5.88 9.85 26 8

systems. It is therefore expected to provide rural areas with high-quality effluents using cost-effective technologies (Seaguret et al., 2000). Trickling filters also encourage oxygenation and removal of carbon dioxide from the water which is important in the case of using the treated effluent for aquaculture (LeKang and Kleppe, 2000). Several factors are important in the function of trickling filters such as hydraulic load, filter media characteristics (type, size, and surface area) and reactors’ dimensions.

The objective of the present research was therefore to evaluate the performance of a mineral filled trickling filter in reducing the concentration of nitrogen and phos-phorous during the treatment of brewery wastewater and to determine the performance of the trickling filter by varying the factors which affects the removal of nitrogen and phosphorous.

MATERIALS AND METHODS

Wastewater sampling and analysis Wastewater samples were collected by filling a cleaned

plastic jerican by holding them just beneath the equa-lizing chamber of the local brewery. They were then transported to the laboratory and analyzed immediately for the selected parameters. A syringe filter of 25 mm diameter (W/0.45 µm cellulose) was used to separate the soluble fraction of the wastewater parameters; whereas for total nitrogen and total phosphorous determination, the wastewater sample was digested by applying the high temperature method. After sample preparations, concen-trations were measured using a Spectrophotometer (Hach Lange Xion 500 LPG385). Table 1 illustrates the physicochemical properties of the wastewater.

Filter material

Lumps of rock approximately sized from 16-32 and 32-64 mm which were placed over the hollow base on a supporting layer sized from 80 to 100 mm was used as the bio filter material. As determined practically, the sizes 16 to 64 mm corresponds to specific surfaces of nearly 72 m

2m

-3 and a hollow space share of 45%. Figure 1

shows the photo of the three size group of trickling filter media. Under operating conditions, nearly 2/3 of this can

Int. J. Appl. Microbiol. Biotechnol. Res. 33

Figure 2. Flow scheme of the experimental setup-pilot scale trickling filter. 1, Wastewater reservoir; 2, fed pump; 3,

trickling filter; 4, sampling ports; 5, draining pump; 6, secondary clarifier; 7, clarified water; 8, recirculation pump; 9, recirculation. Source: Habte Lemji and Eckstädt, 2013.

be assumed to be biologically active (ATV-DVWK-A 281 E, 2001). The gravel stone was placed without long interim storage. During the packing of the filter media, first larger stones are placed then smaller stones and finally filling stones. The filter media was packed in such a way that the largest possible intervening spaces resulted in the trickling filter. In order to ensure that as little abrasion occurs separation is avoided, appropriate handling equipment was used and the drop height not exceeding 500 mm. The abraded matter are removed from the trickling filter by washing with sufficiently large amount of water in order to avoid zones which are impermeable to water and air. Pilot scale trickling filter Experiments were carried out in a cylindrical column reactor (160 cm filling height, 40 cm diam.) with a working volume of 200 L and void ratio of 45%. Wastewater was fed from a storage tank (300 L in volume) and introduced at the top of the reactor. Five sampling ports are located along the trickling filter height at fixed intervals of 26 cm. In order to facilitate a uniform distribution of the wastewater fed to the filter’s free surface at the top of the filter, a sieve plate was installed and a perforated tube connected to the fed pump. It sprays the fed water coiled

placed over it. The wastewater was fed to the reactor after it is been stirred in the storage tank. The treated water from the under drain system enters a secondary clarifier where secondary settlement takes place. There was also a recirculation scheme which returns the effluent back to the trickling filter. Figure 2 illustrates the schematic representation of the pilot scale trickling filter. Trickling filter operation Synthetic brewery wastewater was prepared for this operation of the trickling filter using ammonium sulphate, disodium hydrogen phosphate, ethanol, malt extract, maltose, peptone, sodium hydrogen phosphate and yeast extract as ingredients (Boeije, 1996). Continuous mode of operation with recirculation was the type of operation throughout the experiments. The indigenous microbial population on the trickling filter medium could originate as a near neutral wastewater of the local brewery repeatedly pumped to the trickling filter. Then the multiplication of the microbial population using the synthetic water was performed as synthetic brewery wastewater was used during this investigation. The fed wastewater was intermittently sprayed over the trickling filter continuously at an interval of 1.50 h. Ventilation occurs as a result of the directional buoyancy force which is due to

LL001

M M

M

NSM01

NSM02

NSM03

Outflow

Inflow

18

0 c

m

4

36

7

8

52

1

9

40 cm

Figure 3.1 Flow scheme of the experimental setup-pilot scale trickling filter 1: wastewater reservoir; 2: fed

pump; 3: trickling filter; 4: sampling ports; 5: draining pump; 6: secondary clarifier; 7: clarified water; 8:

recirculation pump; 9: recirculation (Source: Habte Lemji*and Hartmut Eckstädt 2013)

Habte Lemji and Ecktädt 34 temperature differences between the interior and exterior of the trickling filter (Wik, 2003). Temperature and pH were kept varying at 25°C and 6.5 respectively.

In order to avoid channeling effect influent wastewater should be distributed over a medium as uniformly as possible (Wik, 2003). To ensure uniform distribution of water, the end portion of the tube that brings the wastewater was perforated and coiled on top of, the trickling filter after placing a sieve plate. HLR (Lm

-2d

-1)

was calculated as:

HLR = ……………………………………………….(2)

Where Q is the wastewater flow including the recirculation flow (Ld

-1) and A is cross-sectional surface

area of the trickling filter. Mass loading rate (MLR) and mass removal rate (R

mass) of wastewater pollutants were calculated in g m-2

d-1

as:

MLR = ……………………………………..(3)

Rmass = ………………………………(4)

RESULTS AND DISCUSSION Nitrogen and phosphorous acclimation behavior of the trickling filter During the micro-organism immobilization and acclimation process, the synthetic wastewater containing (per 1 liter): 10 g malt extract, 5 g yeast extract, 1.5 g peptone, 8.6 g maltose, 22 g (NH4)2 SO4, 2.8 ml ethanol and buffering salts (NaH2PO4 and Na2H2PO4) was prepared and diluted with tap water to 100 L. Then it is pumped into the reactor continuously with intermittent flow by keeping temperature varying around 25°C and pH near neutral. Concentration of the fed water increased gradually by taking different amount of the concentrated solution and diluting it to 100 L. At the start up, during the formation of biofilms, there might be a need for fixed-film reactors to be inoculated using activated sludge from wastewater treatment plants with suspended growth process (Zhu and Chen, 2002; Green et al., 2006) or attached biofilm from fixed-film reactors. Zhou et al. (2008) used purchased microorganisms created espe-cially for enhancing municipal wastewater microbiology in fixed-film treatment systems. In the present study however, development of bacteria on the trickling filter media was achieved without the need for special inoculation. The gradual increase in concentration of the wastewater and the unique design and operation of

the trickling filter are the reasons for the better achievement of the start up in this research. Yu et al. (2008) reported start-up period of 7 weeks for tested biological aerated filters at 20-26°C. In this research, the trickling filter achieved an average nitrogen and phosphorous removal of about 64 and 44% respectively on 4

th weeks of trickling filter operation with temperature

varying around 22°C. Then after this phase, the full operation of the trickling filter was continued. Influence of hydraulic loading rates The trickling filter exhibited high removal efficiency for total nitrogen at high hydraulic loading rates (4.8 and 6.3 m

3m

-2d

-1) than at low hydraulic loading rates

(4 m

3m

-2d

-1),

and this is due to the increased microbial development and increased activity of microbial population due to the associated increase in organic loading with increase in hydraulic loadings. In addition, the biofilm thickness control at high hydraulic load will reduce the internal diffusion limitation there by enhancing substrate transfer (Westerman

et al., 2000; Vayenas et at., 1997).

Enhancement of aeration at high hydraulic load can also be the other reason that facilitates nitrification. Nevertheless, as attached growth systems maintain a high concentration of microorganisms unlike the other biological treatment methods, high removal rates at relatively small hydraulic retention times is exhibited by the systems. Therefore in general, the effect on the removal efficiency of the trickling filter as hydraulic loading rate changes is not significant. This leads to a conclusion that trickling filter is an ideal treatment technology in time of great variation in wastewater flow which is typically encountered in brewery industry.

Figure 3 portraits the efficiency of the trickling filters for TN and TP removal as a function of hydraulic loading rates. Generally, no special trend for both nitrogen and phosphorous was observed as sometimes there is some sludge in the effluent that contains nitrogen and phosphorous as constituents of the bacterial cells. The maximum removal efficiency of total nitrogen was observed at 4.8 m

3m

-2d

-1, whereas for total phosphorous

it was at 6.3 m3m

-2d

-1. The removal efficiency of total

nitrogen and total phosphorous at the maximum value of hydraulic loading rate, that is, at 6.3 m

3m

-2d

-1 was

75.3±2.27 and 71.80±8.07 in percent respectively. Influence of chemical oxygen demand (COD) load To evaluate the performance of the trickling filter for nutrient removal in time of different chemical oxygen demand (COD) loading, the trickling filter was operated at four different influent COD loadings namely 1160, 1648, 2325 and 3070 mgL

-1. The removal efficiency for both

Int. J. Appl. Microbiol. Biotechnol. Res. 35

N-total P-total 0

20

40

60

80

100

rem

oval effecie

ncy,%

6.3m3m

-2d

-1

5.6 m3m

-2d

-1

4.8 m3m

-2d

-1

4m3m

-2d

-1

Re

mo

val e

ffic

ien

cy (

%)

6.3 m3m-2d-1

5.6 m3m-2d-1

4.8 m3m-2d-1

4 m3m-2d-1

Figure 3. Performance of the trickling filter at different hydraulic loading rate.

N-total P-total0

20

40

60

80

100

120

rem

ova

l e

ffe

cie

ncy,%

1160mgL-1

1648mgL-1

2325mgL-1

3070mgL-1

1160 mgL-1

1648 mgL

-1

2325 mgL-1

3070 mgL

-1

Re

mo

val e

ffic

ien

cy (

%)

Figure 4. performance of the trickling filter at different COD loading.

nitrogen and phosphorous increased with influent COD concentration (Figure 4). But phosphorous exhibited minimum removal efficiency at 2323 mgL

-1 in which the

value is found to be 59.51%. The increase in total nitrogen removal with increase in organic loadings is attributed to the sufficient amount of organic substance for facultative heterotrophic bacteria which are responsible for denitrification. At the maximum influent

COD concentration, the average removal efficiency for total nitrogen was 93.07±2 and for total phosphorous it was 72.45±8 in percent. However, at this high COD loading, the trickling filter tends to develop excess biomass within a short period of time (in about 18 days). Therefore this COD loading was not taken as the optimum but the optimum COD loading is 1163 mgL

-1 at

which the efficiency of removal for total nitrogen and total

Habte Lemji and Ecktädt 36

10 20 30 40 50 60 70 80 90 100 1100

10

20

30

40

50

60

70

80

90

mass r

em

oval ra

te,g

m-2d

-1

mass loading rate,g m-2d

-1

TN

R2=0.97

y=0.77X-1

Mas

s r

em

ova

l rat

e (g m

-2d

-1)

Mass loading rate (g m-2d-1)

Figure 5. The correlation of mass loading rate and mass removal rate as a function of hydraulic loading rate for total nitrogen.

10 20 30 40 50 60 70 80 90 100

0

10

20

30

40

50

60

70

mass r

em

ova

l ra

te,g

m-2d

-1

mass loading rate,gm-2d

-1

y=0.36X-6.2

R2=0.93

TP

Mass loading rate (g m-2d-1)

Mas

s r

em

ova

l rat

e (g m

-2d

-1)

Figure 6. The correlation of mass loading rate and mass removal rate as a

function of hydraulic loading rate for total phosphorous.

phosphorous was 70.6±21.5 and 68.87±8.52% respectively. The uptake of phosphorous in excess of normal bacterial metabolic requirements can be suggested for high phosphorous removal by the trickling

filter. The mechanism of nitrogen removal in the trickling filter is simultaneous nitrification /denitrification.

In Figures 5 and 6, a plot of the removal rate versus loading rate as a function of hydraulic loading rate

Int. J. Appl. Microbiol. Biotechnol. Res. 37

TN TP0

10

20

30

40

50

60

Eff

ecie

ncy,%

45:1:1

62:2:1

62:4:1

61:3:1

45:3:1

Effi

cie

ncy

(%

)

Figure 7. Variations of TN and TP removal efficiency with influent C/N/P ratio.

regarding total nitrogen and total phosphorous removal by the reactor was shown. According to the results, the removal rate showed a strong correlation with the loading rate. The mass removal rate for the two parameters both showed a positive response to the increase (400 to 2400 L m

-2 d

-1) of HLRs: TN from 9.20 to 68.57 g m

-2 d

-1 and TP

from 1.34 to 42.48 g m-2

d-1

. The percentage removal for total phosphorous in this study was 10.45-56.66% as the HLRs changed from 400 to 800 L m

-2 d

-1, and there was

almost no change as the HLRs changed from 1600 to 2400 Lm

-2d

-1 and average Ci was 30.74±7.01 mgL

-1.

(mean±SD). Mass removal rate for TP in this study ranged from

1.34 to 12.06 (mass loading rate from 12.20 to 24.41 g m-

2 d

-1), influenced significantly by increasing MLR and it

was ranged from19.25 to 42.48 gm-2

d-1

(mass loading rate from 48.82 to 73.22 gm

-2d

-1), influenced slightly by

increasing MLR. As a result of this trend, efficiency of removal for PT increased as the HLRs changed from 400 to 800 L m

-2 d

-1 and there were almost no change as

HLRs changes from 1600 to 2400 L m-2

d-1

. The removal efficiency for total nitrogen ranged from 71.8 to 86.59 as the HLRs increased from 400 to 800 L m

-2d

-1, and it was

ranged from 65.46 to 75.3 as the HLRs changed from 1600 to 2400 Lm

-2d

-1 at average Ci of 36.9±11.09

(mean±SD). The mass removal rate for TN was from 9.20 to 68.57, influenced slightly by increasing MLR. Therefore the change in efficiency of the trickling filter for total nitrogen removal has shown only small difference as the

HLRs changes from 400 to 2400 Lm-2

d-1

. Influence of pH on the trickling filter performance The performance of the trickling filter for the selected parameters as a function of different wastewater pH was investigated in this study. With regard to the removal of ammonium nitrogen and total phosphorous, the trickling filter showed maximum removal efficiency at near neutral pH. As the pH increased from 5.65 to 6.3, the removal efficiency for ammonium nitrogen increased from 55.5 to 95.6 and for that of total phosphorous it increased from 36 to 70%. The degree of total nitrogen removal conver-sion achieved after three consecutive operation days of the trickling filter at pH 8.3 was 82.73% compared to 40.73 and 10.01% at pH 8 and 9, respectively. As the finding here is connected to the previous investigation, the trickling filter had maximum efficiency for COD removal in this same range of pH which means high removal efficiency for both organics and nutrients can be achieved at the same pH condition which is a desirable property for the real scale application of the trickling filter. Influence of carbon: nitrogen: phosphorus ratios The aim of conducting the experiment in which the result of the investigation is shown in Figure 7 is to evaluate

Habte Lemji and Ecktädt 38

1 2 3 4 5 6 7 80,0

0,2

0,4

0,6

0,8

1,0

Concentr

ation,m

gL

-1

Time,d

influent

effluent

Time (days)

Co

nce

ntr

atio

n (m

gL-1

) Influent

Effluent

0.0

0.2

0.4

0.6

0.8

1.0

Figure 8. Nitrite concentration in the influent and effluent of the trickling filter.

how the trickling filter responds with regard to both total nitrogen and total phosphorus removal when the influent C/N/P ratio is varied as given in the experiment. However, this does not represent the overall efficiency of the trickling filter. The operation of the trickling filter at different C: N: P ratio was carried out while keeping all the other operating conditions constant. A flow rate of 300 L per day, temperature varying at 20°C and pH varying at 7 was the operating condition. The variation in total nitrogen removal efficiency with the different ratio was great; whereas in case of total phosphorus removal, there was only small variation. The optimum C: N: P ratio was 62:4:1 in which the removal (%) of COD, nitrogen and phosphorus was 85.5, 61.87 and 37.5 respectively.

Performance at steady state biofilm state of the trickling filter was evaluated for each selected parameters at constant operating conditions. For influent total nitrogen of around 39.63 mgL

-1, total nitrogen effluent value in the

range of 2.9−27.8 mgL-1

was achieved. At this constant operation condition, the biofilm status come to near stability and after operating the trickling filter for about 4 weeks, constant removal efficiency for total nitrogen varying around 88% was recorded. With regard to total phosphorous removal for an inlet concentration of 10.92 mgL

-1, effluent value in the range of 1.8−7.16 mgL

-1 was

achieved, and at the steady state biofilm state, total phosphorous removal efficiency was varied at 80%. Influent ammonium nitrogen varied at about 22.54 mgL

-1

and effluent ammonium nitrogen value in the range of 0.2−13.6 mgL

-1 was achieved as a result. As nitrifying

bacteria well developed on the trickling filter medium with

time, a near to 100% removal efficiency of ammonium nitrogen was achieved at this steady state. Figures 8 and 9 illustrate the influent and effluent nitrite and nitrate concentration. The absence of high nitrite or nitrate level in the effluent indicates denitrification has occurred in the bioreactor. For the determination of the parameters after each designed experiment was performed, the influent and effluent samples collected and kept in a refrigerator were analyzed for the selected parameters three times per week unless otherwise indicated; whereas pH and temperature measurements were made daily. Figures 10 to 12 illustrate the performance of the trickling filter for total nitrogen, ammonium nitrogen and total phosphorous at constant COD concentration (nearly 1000 mgL

-1) and

constant hydraulic loading (300 L-1

d-1

). Whereas Figure 13 portraits the efficiency of the trickling filter for all parameters.

As a rationally for the overall good performance of the trickling filter for nitrogen removal which is otherwise unlikely to occur at the present COD content of the feed water, one can justify as; the high volume of packed filter medium (0.2 m

3) which is as large as enough for the

accommodation of both the nitrifying bacteria and organic carbon removing bacteria, could be one reason that favors nitrification. High sludge concentration is maintained in the trickling filter which ensured the low food to microorganism ratio so that nitrification is favored regardless of the increased organic carbon. The other most probable reason for this is increased biofilm thickness as a result of the high COD loadings which bring about the coexistence of both the heterotrophs and

Int. J. Appl. Microbiol. Biotechnol. Res. 39

2 4 6 8 100,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40 influent

effluentconcentr

ation,m

gL

-1

Time,d

Co

nce

ntr

atio

n (m

gL-1

) Effluent

0.40

Time (days)

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

Influent

Figure 9. Nitrate concentration in the influent and effluent of the trickling filter.

0 2 4 6 8 10 12 14 16 18 200

5

10

15

20

25

30

35

40

45

50

Co

nce

ntr

atio

n,m

gL

-1

Time,d

Influent

Effluent

Time (days)

Co

nce

ntr

atio

n (m

gL-1

)

Figure 10. Total nitrogen influent and effluent concentration of the trickling filter.

Habte Lemji and Ecktädt 40

0 2 4 6 8 10 12 14 16 180

5

10

15

20

25C

once

ntr

atio

n,m

gL-1

Time,d

Influent

Effluent

Time (days)

Co

nce

ntr

atio

n (m

gL-1

)

Figure 11. Influent and effluent ammonium nitrogen concentration of the trickling filter.

0 2 4 6 8 10 120

2

4

6

8

10

12

14

Concentr

ation,m

gL

-1

Time,d

Influent

Effluent

Time (days)

Co

nce

ntr

atio

n (m

gL-1

)

Figure 12. Influent and effluent total phosphorous concentration.

Int. J. Appl. Microbiol. Biotechnol. Res. 41

N-total P-total NH4-N0

10

20

30

40

50

60

70

80

90

100

rem

ova

l eff

eci

ency

,%

Re

mo

val e

ffic

ien

cy (%

)

P‒total NH4‒N N‒total Figure 13. Overall performance of the trickling filter for the selected parameter.

autotrohrophs because the food to microorganism ratio is lower in the lower section of the biofilm that favors the nitrifiers. Conclusion The results of the present investigation showed that with regard to total nitrogen removal, the efficiency of the trickling filter was not affected significantly by the given range of hydraulic load that is, 900 to 1100 Ld

-1, and that

an average removal efficiencies ranging from 65.46 to 86.59% could be achieved at influent COD concentration of 1000 mgL

-1. Under normal circumstances, nitrification

is unlikely to occur at high organic carbon loadings; however this investigation found significant reduction in nitrogen due to some reasons given in the discussion section. High value of organic nitrogen removal by the reactor even in time of organic shock loads could also be achieved by the reactor as seen from the result of the operation at different COD loadings. Performance of the bioreactor for removal of nitrogen as the COD load varies could not be affected significantly. The bioreactor can achieve a steady biofilm state with regard to total nitrogen removal when the reactor operated constantly with the optimum operating condition. The trickling filter could achieve as high as 98% removal efficiency with regard to removing total nitrogen from the wastewater at steady state biofilm state.

In removing phosphorous, the trickling filter has performed about 50% as the wastewater flow rate changes from 900 to 1100 Ld

-1 but had no significant

effect except at hydraulic load of 1100 Ld-1

. With regard to different COD load, the bioreactor could achieve removal efficiencies which in most time only slightly varied, could achieve removal efficiency as high as 74.69%. When the COD load is 1648 mgL

-1, about 75%

total phosphorous removal could be achieved by the trickling filter at a flow rate of 1100 Ld

-1. The bioreactor

could reach a steady state biofilm state achieving more or less constant phosoprous removal efficiency. At the steady state biofilm state, the trickling filter could achieve average removal efficiency of about 80%. The uptake of phosphorous in excess of normal bacterial metabolic requirements could be suggested for the high phosphorous removal by the bioreactor. Significant reduction of both nitrogen and phosphorous can be achieved together with significant COD reduction as long as the present design and operation conditions is adopted.

ACKNOWLEDGEMENTS

This research was funded by the LANDESZENTRALKASSE M-V STIPENDIUM (grant number 7117130625602). We would also like to acknowledge the contribution of Mr. Mathias Wachsmuth for his assistance in constructing the pilot scale trickling filter.

Compliance with ethics guidelines

The authors declare that they have no conflict of interest.

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