**4. Case study 1: Pig slurry treatment**

Fig. 7 to Fig. 10 illustrate the comparison of the water characteristics during the experiments. COD, BOD and NH4 + -N values are presented as a proportion between their concentration in certain moment and its initial concentration (CODt / COD0, BODt / BOD0 and NH4 + -Nt / NH4 + -N0).

During the first 3 days a significant decreasing of COD concentration was observed, especially in the ASR and in the hybrid installation ASR-SSVFW (fig. 7). This is a result of the additional aeration in the ASR. Until this moment the extent of COD decreasing in the ASR, SSVFW and hybridinstallationASR-SSVFWwas: 58.9%, 39%and49.8%.Afterthattheprocess slowsdown. Duringthisperiodeasierchemicallyoxidizableorganicmatterandbiodegradableorganicmatter undergo changes under the influence of the oxygen and microbial activity. In the SSVFW the decreasing of the COD becomes slower because there is not additional aeration and the plants roots are the only suppliers of oxygen. During the first 3 days the COD concentration decreas‐ inginthehybridinstallationis almostidenticalwiththatintheASR,but afterwastewaterinflow to the SSVFW of the hybrid installation, the tenor of the decreasing curve of the COD concentra‐ tion lightly altered and reached that in the SSVFW. Due to the preliminary pig slurry dilution in the lab-scale including only subsurface vertical flow wetland, the initial concentrations of the analyzed parameters were almost twice lower than those in the other two experiments. That is whythewaterpurificationintheSSVFWis fasterthanthatinthecombinedsystem.Thereaching of the standards of measured physicochemical characteristic in the SSVFW, ASR and hybrid installation ASR-SSVFW becomes for twelve, then and sixteen days, respectively. Significant extent of the COD concentration decreasing in the three systems was achieved: in SSVFW - 93.1 %, in ASR 96.7 % and in hybrid installation ASR-SSVFW 97.1 %.

BOD decreasing in these systems becomes without significant differences and lightly in comparison with that of the COD decreasing (fig. 8). Under aeration BOD values in ASR and ASR-SSVFW, are decreasing a little bit fully in comparison with that in the SSVFW. During the first 3 days the decreasing extents of the BOD values in the three installations are: SSVFW - 43.3 %, ASR – 61.8 % and hybrid installation ASR-SSVFW – 54.2 %. The reaching of the standards in the SSVFW, ASR and ASR-SSVFW becomes for twelve, ten and sixteen days, respectively.

**Figure 8.** BOD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

a major part of biomass, e.g. 12.4 % of C5H7O2N mass being nitrogen [84].

In parallel with the decreasing of ammonium-nitrogen concentration, an increasing of nitratenitrogen is observed, as a result of the nitrification (fig. 10). In the ASR that becomes faster in comparison with the process in the SSVFW and hybrid installation ASR-SSVFW. During the 5th day was observed equalization of the nitrate-nitrogen concentration in the ASR and SSVFW. Elimination of the nitrate-nitrogen was not achieved during the wastewater purification in

The nitrogen is one of the main pollutants in wastewater that can cause eutrophication, affects dissolved oxygen levels of receiving water, and may cause toxicity (depending on the nitrogen form) to the aquatic organisms [83]. In these systems the transformation and removal of nitrogen are accomplished by both classical and newly discovered routes. The classical pathways include biological i.e. ammonification, nitrification, denitrification, plant uptake, biomass assimilation, dissimilatory nitrate reduction), and physicochemical routes (e.g. ammonia volatilization and adsorption). The newly discovered nitrogen removal routes are solely dependent on microbiological metabolism such as partial nitrification-denitrification. The decreasing of ammonium - nitrogen in the systems is shown on Fig. 9. The similar effect was observed. During the first three days of the purification process in these three systems was observed elimination of significant part of the ammonium – nitrogen: SSVFW – 53.7 %, ASR – 100 % and in the hybrid installation ASR-SSVFW – 93.7 %. This process is slower in the SSVFW because of insufficient oxygen concentration in the column matrix. Fully elimination of the ammonium - nitrogen in ASR was achieved for three days and for twelve days in the SSVFW. In the hybrid installation this was achieved for seven days. The decreasing of ammonium – nitrogen can be common result of volatilization, nitrification, plant uptake in wetland system and immobilization onto microbial cells. It is believed that nitrogen constitutes

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**Figure 7.** COD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

**Figure 8.** BOD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

During the first 3 days a significant decreasing of COD concentration was observed, especially in the ASR and in the hybrid installation ASR-SSVFW (fig. 7). This is a result of the additional aeration in the ASR. Until this moment the extent of COD decreasing in the ASR, SSVFW and hybridinstallationASR-SSVFWwas: 58.9%, 39%and49.8%.Afterthattheprocess slowsdown. Duringthisperiodeasierchemicallyoxidizableorganicmatterandbiodegradableorganicmatter undergo changes under the influence of the oxygen and microbial activity. In the SSVFW the decreasing of the COD becomes slower because there is not additional aeration and the plants roots are the only suppliers of oxygen. During the first 3 days the COD concentration decreas‐ inginthehybridinstallationis almostidenticalwiththatintheASR,but afterwastewaterinflow to the SSVFW of the hybrid installation, the tenor of the decreasing curve of the COD concentra‐ tion lightly altered and reached that in the SSVFW. Due to the preliminary pig slurry dilution in the lab-scale including only subsurface vertical flow wetland, the initial concentrations of the analyzed parameters were almost twice lower than those in the other two experiments. That is whythewaterpurificationintheSSVFWis fasterthanthatinthecombinedsystem.Thereaching of the standards of measured physicochemical characteristic in the SSVFW, ASR and hybrid installation ASR-SSVFW becomes for twelve, then and sixteen days, respectively. Significant extent of the COD concentration decreasing in the three systems was achieved: in SSVFW - 93.1

BOD decreasing in these systems becomes without significant differences and lightly in comparison with that of the COD decreasing (fig. 8). Under aeration BOD values in ASR and ASR-SSVFW, are decreasing a little bit fully in comparison with that in the SSVFW. During the first 3 days the decreasing extents of the BOD values in the three installations are: SSVFW - 43.3 %, ASR – 61.8 % and hybrid installation ASR-SSVFW – 54.2 %. The reaching of the standards in the SSVFW, ASR and ASR-SSVFW becomes for twelve, ten and sixteen days, respectively.

**Figure 7.** COD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

%, in ASR 96.7 % and in hybrid installation ASR-SSVFW 97.1 %.

76 Applied Bioremediation - Active and Passive Approaches

The nitrogen is one of the main pollutants in wastewater that can cause eutrophication, affects dissolved oxygen levels of receiving water, and may cause toxicity (depending on the nitrogen form) to the aquatic organisms [83]. In these systems the transformation and removal of nitrogen are accomplished by both classical and newly discovered routes. The classical pathways include biological i.e. ammonification, nitrification, denitrification, plant uptake, biomass assimilation, dissimilatory nitrate reduction), and physicochemical routes (e.g. ammonia volatilization and adsorption). The newly discovered nitrogen removal routes are solely dependent on microbiological metabolism such as partial nitrification-denitrification.

The decreasing of ammonium - nitrogen in the systems is shown on Fig. 9. The similar effect was observed. During the first three days of the purification process in these three systems was observed elimination of significant part of the ammonium – nitrogen: SSVFW – 53.7 %, ASR – 100 % and in the hybrid installation ASR-SSVFW – 93.7 %. This process is slower in the SSVFW because of insufficient oxygen concentration in the column matrix. Fully elimination of the ammonium - nitrogen in ASR was achieved for three days and for twelve days in the SSVFW. In the hybrid installation this was achieved for seven days. The decreasing of ammonium – nitrogen can be common result of volatilization, nitrification, plant uptake in wetland system and immobilization onto microbial cells. It is believed that nitrogen constitutes a major part of biomass, e.g. 12.4 % of C5H7O2N mass being nitrogen [84].

In parallel with the decreasing of ammonium-nitrogen concentration, an increasing of nitratenitrogen is observed, as a result of the nitrification (fig. 10). In the ASR that becomes faster in comparison with the process in the SSVFW and hybrid installation ASR-SSVFW. During the 5th day was observed equalization of the nitrate-nitrogen concentration in the ASR and SSVFW. Elimination of the nitrate-nitrogen was not achieved during the wastewater purification in these systems. The reason for impossibility of nitrate-nitrogen removal is the lack of anoxic conditions in the systems. It is also well established that carbon availability plays an important role in both synthesis and activity of denitrifying enzymes as well as general support of the denitrifying population [85]. The lack of organic carbon source is supposed to keep insignifi‐ cant denitrification. There are two required conditions for denitrification: anoxic environment and sufficient organic carbon source. In the ASR this process does not occur, because there is aeration. In constructed wetland system the bottom layer provides anoxic conditions for achieving a denitrification. Hence, initial high ammonium-nitrogen concentrations and deficient of organic carbon source were the reasons to depress the denitrification in the wetland system treated the pig wastewater.

efficiency in the landfill leachate on the third day in the SSVFW is 24 %, in the ASR it is 51.5 % and in the hybrid system ASR-SSVFW it is 51 %. The COD reduction is smooth and without significant fluctuations. The limit concentration of COD in the SSVFW was reached for 15 days, in the ASR for 9 days and in the hybrid installation ASR-SSVFW for 12 days. The removal

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**Figure 10.** Nitrate-nitrogen in the water samples from SSVFW, ASR and integrated installation ASR-SSVFW

**Figure 11.** COD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

efficiency is 98 %, 97.8 % and 97.9 %, respectively.

**Figure 9.** Ammonium-nitrogen in the water samples from SSVFW, ASR and hybrid installation ASR-SSVFW

During the first two days the odour of the treated wastewater in the systems was eliminated. The pH values of the wastewater are in the neutral zone (6.3 – 8.3).

### **5. Case study 2: Landfill leachate treatment**

Fig. 11 to Fig. 14 illustrate the comparison of the water characteristics during the experiments. COD, BOD and NH4 + -N values are presented like proportion between their concentration in certainmomentandits initial concentration(CODt /COD0,BODt /BOD0 andNH4 + -Nt /NH4 + -N0).

During the experiments the COD decreasing in these three systems is similar (fig. 11). The reduction of the COD was slightly faster with the preliminary aerobic treatment of the landfill leachate. During the first three days there was a significant decrease of COD. The removal

these systems. The reason for impossibility of nitrate-nitrogen removal is the lack of anoxic conditions in the systems. It is also well established that carbon availability plays an important role in both synthesis and activity of denitrifying enzymes as well as general support of the denitrifying population [85]. The lack of organic carbon source is supposed to keep insignifi‐ cant denitrification. There are two required conditions for denitrification: anoxic environment and sufficient organic carbon source. In the ASR this process does not occur, because there is aeration. In constructed wetland system the bottom layer provides anoxic conditions for achieving a denitrification. Hence, initial high ammonium-nitrogen concentrations and deficient of organic carbon source were the reasons to depress the denitrification in the wetland

**Figure 9.** Ammonium-nitrogen in the water samples from SSVFW, ASR and hybrid installation ASR-SSVFW

The pH values of the wastewater are in the neutral zone (6.3 – 8.3).

**5. Case study 2: Landfill leachate treatment**

+

COD, BOD and NH4

During the first two days the odour of the treated wastewater in the systems was eliminated.

Fig. 11 to Fig. 14 illustrate the comparison of the water characteristics during the experiments.

During the experiments the COD decreasing in these three systems is similar (fig. 11). The reduction of the COD was slightly faster with the preliminary aerobic treatment of the landfill leachate. During the first three days there was a significant decrease of COD. The removal

certainmomentandits initial concentration(CODt /COD0,BODt /BOD0 andNH4


+


+ -N0).

system treated the pig wastewater.

78 Applied Bioremediation - Active and Passive Approaches

**Figure 10.** Nitrate-nitrogen in the water samples from SSVFW, ASR and integrated installation ASR-SSVFW

efficiency in the landfill leachate on the third day in the SSVFW is 24 %, in the ASR it is 51.5 % and in the hybrid system ASR-SSVFW it is 51 %. The COD reduction is smooth and without significant fluctuations. The limit concentration of COD in the SSVFW was reached for 15 days, in the ASR for 9 days and in the hybrid installation ASR-SSVFW for 12 days. The removal efficiency is 98 %, 97.8 % and 97.9 %, respectively.

**Figure 11.** COD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

The preliminary dilution with tap water of the landfill leachate and the flowing into the SSVFW, lead to almost double decrease of the BOD. BOD decreasing in the wetland system is smoother compared to the ASR and the hybrid installation (fig. 12). The removal efficiency during the first three days is 46.8 % in the SSVFW, 72.2 % in the ASR and 71.4 % in the hybrid installation ASR-SSVFW. The limiting concentration for BOD in the SSVFW was achieved in 11 days with 92.9 % removal efficiency, in the ASR – 6 days with 95.4 % removal efficiency and in the ASR-SSVFW respectively in 9 days with 94.5 % removal efficiency.

due to the insufficient quantity of the source of organic carbon in the wetland system [85] and

+-N decreasing in the water samples from SSVFW, ASR and hybrid installation ASR-SSVFW

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During the experiments pH decreased slightly from 8,3 to 7,5. The neutralization of the landfill leachate was achieved during the preliminary dilution with tap water, while in the hybrid


on the other hand - the aerobic conditions in the aerobic bioreactor.

installation it was achieved during the third day of operation.

**Figure 14.** [NO3

**Figure 13.** NH4


**Figure 12.** BOD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

The preliminary dilution of the wastewater and the flowing into the SSVFW, resulted in double decrease of the concentration of the [NH4 + -N]. As shown on Fig. 13 a sharp decrease of the [NH4 + -N] concentration in the first three days occurs in the systems where preliminary aerobic treatment of the landfill leachate was used. The removal efficiency in the SSVFW is 74.8 %, in the ASR 99.6 % and in the ASR-SSVFW 96.2 %. This is probably due to the air blowing into the aerobic reactor to support microbial activity. On the other hand this intensive aeration can cause the escape of ammonia from the system.

Complete removal of the [NH4 + -N] in the SSVFW was achieved for 10 days while in the ASR it was for 4 days and in the ASR-SSVFW - for 5 days. This can be explained by the fact that in this reactor the oxygen is not enough for the nitrification and from the constructive point of view the separation of ammonia from the system is embarrassed.

The aerobic treatment of the landfill leachate in the reactor with suspended activated sludge results in a significant accumulation of nitrate ions in comparison with the process taking place in the wetland system where preliminary diluted landfill leachate is treated (Fig. 14). In the laboratory systems an accumulation of the nitrate ions was observed. Probably this effect is

The preliminary dilution with tap water of the landfill leachate and the flowing into the SSVFW, lead to almost double decrease of the BOD. BOD decreasing in the wetland system is smoother compared to the ASR and the hybrid installation (fig. 12). The removal efficiency during the first three days is 46.8 % in the SSVFW, 72.2 % in the ASR and 71.4 % in the hybrid installation ASR-SSVFW. The limiting concentration for BOD in the SSVFW was achieved in 11 days with 92.9 % removal efficiency, in the ASR – 6 days with 95.4 % removal efficiency and

in the ASR-SSVFW respectively in 9 days with 94.5 % removal efficiency.

**Figure 12.** BOD decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

decrease of the concentration of the [NH4

80 Applied Bioremediation - Active and Passive Approaches

cause the escape of ammonia from the system.

+

view the separation of ammonia from the system is embarrassed.

Complete removal of the [NH4

[NH4 +

The preliminary dilution of the wastewater and the flowing into the SSVFW, resulted in double

it was for 4 days and in the ASR-SSVFW - for 5 days. This can be explained by the fact that in this reactor the oxygen is not enough for the nitrification and from the constructive point of

The aerobic treatment of the landfill leachate in the reactor with suspended activated sludge results in a significant accumulation of nitrate ions in comparison with the process taking place in the wetland system where preliminary diluted landfill leachate is treated (Fig. 14). In the laboratory systems an accumulation of the nitrate ions was observed. Probably this effect is




+

**Figure 13.** NH4 +-N decreasing in the water samples from SSVFW, ASR and hybrid installation ASR-SSVFW

due to the insufficient quantity of the source of organic carbon in the wetland system [85] and on the other hand - the aerobic conditions in the aerobic bioreactor.

During the experiments pH decreased slightly from 8,3 to 7,5. The neutralization of the landfill leachate was achieved during the preliminary dilution with tap water, while in the hybrid installation it was achieved during the third day of operation.

**Figure 14.** [NO3 - -N] decreasing of the water samples in SSVFW, ASR and hybrid installation ASR-SSVFW

In Table 2 are compared the data characterized the two studied wastewaters that are treated in ASR, SSVFW and hybrid installation ASR-SSVFW. The data are compared with the standards in Bulgaria (Benchmarks). Obviously, the requirements of the national standards were met.

The elimination of BOD occurs fast in most cases during the initial five days. The efficiency of BOD removal at recirculation ratio 1:1 was 72 %, 85 % and 92 % for flow rate 82 ml min-1, 60 ml min-1 and 40 ml min-1, respectively. At recirculation ratio 1:2 it was 83 %, 92 % and 93 % for the corresponding flow rates. The efficiency was 91 % at flow rate 82 ml min-1 and recirculation ratio1:3. The same efficiency was obtained after 4 days at flow rate 60 ml min-1 and after 3 days at flow rate 40 ml min-1. It was observed that the longer the water remained quiet in SSVFW,

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**Figure 15.** Comparison of the COD and BOD values of the treated landfill leachate at different flow rates

the faster COD and BOD decreased.


**Table 2.** Characteristics of the influent and the effluents from the three systems

The flow rate is one of the important factors, which control the performance of subsurface vertical flow wetland systems. The higher flow rate promotes faster passage of wastewater through the media, thus reducing the optimum contact time and leads to longer period needed for treatment [74]. The recirculation of the treated wastewater through the subsurface verticalflow wetland also has a significant role in the purification efficiency [74, 87-88]. For confirma‐ tion of these statements experiments with three different wastewater flow rates (40, 60 and 82 ml/min) and three different recirculation ratios (1:1, 1:2 and 1:3) were conducted. The hydraulic retention time in the wetland system was 1.8, 1.2 and 0.9 h, respectively.

The comparison of the COD and BOD values of the treated landfill leachate during the experiments is illustrated in fig.15. The data demonstrate the influence of the recirculation at the three different flow rates on the treatment ability of the lab-scale vertical-flow wetland system. The decreasing of COD values after five days from the beginning is fast. Then the process slows down. The efficiency at the 5th day (recirculation ratio 1:1) was 67 % at flow rate 82 ml min-1, 81 % - at flow rate 60 ml min-1 and 90 % - at flow rate 40 ml min-1. The efficiency at recirculation ratio 1:2 was 78 %, 86 % and 90 %, respectively, and at recirculation ratio 1:3 it was 78 %, 90 % and 96 %, respectively. COD decreased slower when the flow rate was higher. The elimination of BOD occurs fast in most cases during the initial five days. The efficiency of BOD removal at recirculation ratio 1:1 was 72 %, 85 % and 92 % for flow rate 82 ml min-1, 60 ml min-1 and 40 ml min-1, respectively. At recirculation ratio 1:2 it was 83 %, 92 % and 93 % for the corresponding flow rates. The efficiency was 91 % at flow rate 82 ml min-1 and recirculation ratio1:3. The same efficiency was obtained after 4 days at flow rate 60 ml min-1 and after 3 days at flow rate 40 ml min-1. It was observed that the longer the water remained quiet in SSVFW, the faster COD and BOD decreased.

In Table 2 are compared the data characterized the two studied wastewaters that are treated in ASR, SSVFW and hybrid installation ASR-SSVFW. The data are compared with the standards in Bulgaria (Benchmarks). Obviously, the requirements of the national standards

> **Bench marks**

ASR SSVFW ASR-SSVFW ASR SSVFW

**Average efficiency, %**

Pig slurry

Landfill leachate

70 95.6 11 12 12 16 10 12

15 97.5 9 10 10 9 9 11

10 - - - - - - -

Pig slurry

Landfill leachate

**Time, days**

ASR-SSVFW

Pig slurry

Landfill leachate

were met.

**Paramet er**

**COD, mg L-1**

**BOD, mg L-1**

**NH4 +-N, mg L-1**

**NO3 - -N, mg L-1**

Pig slurry

1535 ± 502

612 ± 419

322 ± 87

**pH** 7.2 ± 1.1 7.9 ± 0.4

Landfill leachate

2940 ± 140

230.5 ± 26.5

206.7 ± 8.3

0 1.5 ± 0.4

**Influent Effluent**

82 Applied Bioremediation - Active and Passive Approaches

Pig slurry

72.4 ± 7.1

14.4 ± 0.4

16.7 ± 0.3

> 7.1 ± 0.1

Landfill leachate

69 ± 1

15.6 ± 0.7

16.5 ± 0.5

> 7.2 ± 0.1

**Table 2.** Characteristics of the influent and the effluents from the three systems

Pig slurry

69.3 ± 3.9

15.7 ± 1.5

16.9 ± 0.1

> 7.2 ± 0.1

retention time in the wetland system was 1.8, 1.2 and 0.9 h, respectively.

Landfill leachate

67.5 ± 11.5

14.5 ± 0.5

> 17 ± 0.1

7.2 ± 0.1

Pig slurry

63.6 ± 4

15.8 ± 0.4

15.9 ± 0.6

7.1 ± 0.1

The flow rate is one of the important factors, which control the performance of subsurface vertical flow wetland systems. The higher flow rate promotes faster passage of wastewater through the media, thus reducing the optimum contact time and leads to longer period needed for treatment [74]. The recirculation of the treated wastewater through the subsurface verticalflow wetland also has a significant role in the purification efficiency [74, 87-88]. For confirma‐ tion of these statements experiments with three different wastewater flow rates (40, 60 and 82 ml/min) and three different recirculation ratios (1:1, 1:2 and 1:3) were conducted. The hydraulic

The comparison of the COD and BOD values of the treated landfill leachate during the experiments is illustrated in fig.15. The data demonstrate the influence of the recirculation at the three different flow rates on the treatment ability of the lab-scale vertical-flow wetland system. The decreasing of COD values after five days from the beginning is fast. Then the process slows down. The efficiency at the 5th day (recirculation ratio 1:1) was 67 % at flow rate 82 ml min-1, 81 % - at flow rate 60 ml min-1 and 90 % - at flow rate 40 ml min-1. The efficiency at recirculation ratio 1:2 was 78 %, 86 % and 90 %, respectively, and at recirculation ratio 1:3 it was 78 %, 90 % and 96 %, respectively. COD decreased slower when the flow rate was higher.

Landfill leachate

62.5 ± 4.5

15.7 ± 0.8

> 17 ± 0.1

7 ± 0.1 6.0 – 8.5

0 0 0 0 0 0 2 100 7 6 10 10 8 8

**Figure 15.** Comparison of the COD and BOD values of the treated landfill leachate at different flow rates

The influence of these parameters on the ammonium depletion is illustrated in Fig. 16. It was exhausted completely during the experiments. The decrease of ammonium-nitrogen could be collective result of volatilization, nitrification, plant uptake in wetland system and immobili‐

ratios. In all cases the values increased during the first 1-2 days. After this period the curves

faster when the flow rate was lower. The influence of the recirculation ratios was opposite. During the experiments at different conditions dissolved oxygen was measured and the values were from 5.2 to 8 mg L-1. It is known that the concentration of 1 mg L-1 is sufficient for oxidation

The lack of the denitrification during the treatment can be a result of the less activity of denitrifying bacteria in the system. Vymazal reported that SSVFW removes successfully

Phosphorus removal in wetland treatment systems occurs through adsorption, plant uptake, complexation, and precipitation [92]. The value of total phosphorus (TP) in the treated leachate was relatively low (5.5 mg L-1). It was established that TP removal follows the same tendency

The higher flow rate leads to a longer period of elimination of TP. At the same time the change of the recirculation ratio from 1:1 to 1:3 (water stays quiet in SSVFW longer) leads to shorter period of elimination (e.g. at flow rate 82 ml min-1 the TP removal was 41.8 %, 60 % and 67.3

It was established that during the experiments with different flow rate and hydraulic retention time pH slightly decreased from 7.9 to 7.5 and the salinity also decreased from 2.5 to 1.9 ‰. TDS gradually decreased from 2460 to 1778 mg L-1. The values of TSS varied from 1.91 to 3.96 g L-1. Landfill leachate conductivity decreased from 4710 to 3408 μS cm-1. TDS, TSS, salinity, phosphorus concentration as well as the conductivity have been determined only for the case

It is well known that the vegetation in the wetland systems play a significant role in purification process. Aquatic plants enhance nutrient removal through biomass accumulation, fixation of inorganic and organic particles and where ammonium-N is present, by the creation of an oxidized rhizosphere [93]. In the absence of plants, the gravel substrate provided significant wastewater treatment [94, 95], although most studies report improved nutrient removal where plants are present [96]. Our experiments without vegetation in the lab-scale subsurface vertical-flow wetland system leads to lower treatment efficiency in comparison whit that where in the laboratory system has grown vegetation (Fig. 18). That confirms the important role of the plants in purification process. On the other hand the lack of plants allows the use of additional organic carbon source, which achieves a denitrification process (Fig. 19). In these experiment was added methanol in the SSVFW without vegetation. As a result was observed

% for 1:1, 1:2 and 1:3 recirculation ratios during 8, 6 and 4 days, correspondingly).




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85

zation. At the same time NO3

of ammonium [90].

NH4 +

as NH4 + -

shape depended on the experimental conditions. The concentration of NO3

sources is thought to prevent significant levels of denitrification [85].

of landfill leachate at different flow rate and hydraulic retention time.

decreasing of the nutrition elements and their elimination from the system.

**Figure 16.** Comparison of the [NH4 +-N] and [NO3 - -N] values of the treated landfill leachate at different flow rates

The importance of nitrogen removal is comparable with that for organic carbon, toxic com‐ pounds and metals removal during the leachate treatment in SSVFW. Ammonium removal by nitrification in constructed wetlands differing in design and purpose was reported [89]. It is known that autotrophic nitrification consists of two successive aerobic reactions, the conver‐ sion of ammonium to nitrite by ammonium oxidizing bacteria and the conversion of nitrite to nitrate by nitrite oxidizing bacteria. The concentration of ammonium-nitrogen in the influent used in this study was relatively high. So, it was interesting to record the changes of NH4 + -N and NO3 - -N values during the leachate treatment at different flow rates and recirculation ratios. The influence of these parameters on the ammonium depletion is illustrated in Fig. 16. It was exhausted completely during the experiments. The decrease of ammonium-nitrogen could be collective result of volatilization, nitrification, plant uptake in wetland system and immobili‐ zation. At the same time NO3 - -N increased depending on the flow rate and the recirculation ratios. In all cases the values increased during the first 1-2 days. After this period the curves shape depended on the experimental conditions. The concentration of NO3 - -N has increased faster when the flow rate was lower. The influence of the recirculation ratios was opposite. During the experiments at different conditions dissolved oxygen was measured and the values were from 5.2 to 8 mg L-1. It is known that the concentration of 1 mg L-1 is sufficient for oxidation of ammonium [90].

The lack of the denitrification during the treatment can be a result of the less activity of denitrifying bacteria in the system. Vymazal reported that SSVFW removes successfully NH4 + -N but the denitrification is very limited in these systems [91]. It was also well established that carbon availability plays an important role in both synthesis and activity of denitrifying enzymes as well as general support of the denitrifying population. The lack of organic carbon sources is thought to prevent significant levels of denitrification [85].

Phosphorus removal in wetland treatment systems occurs through adsorption, plant uptake, complexation, and precipitation [92]. The value of total phosphorus (TP) in the treated leachate was relatively low (5.5 mg L-1). It was established that TP removal follows the same tendency as NH4 + -N removal. During the first two days a significant TP elimination occured (Fig.17). The higher flow rate leads to a longer period of elimination of TP. At the same time the change of the recirculation ratio from 1:1 to 1:3 (water stays quiet in SSVFW longer) leads to shorter period of elimination (e.g. at flow rate 82 ml min-1 the TP removal was 41.8 %, 60 % and 67.3 % for 1:1, 1:2 and 1:3 recirculation ratios during 8, 6 and 4 days, correspondingly).

It was established that during the experiments with different flow rate and hydraulic retention time pH slightly decreased from 7.9 to 7.5 and the salinity also decreased from 2.5 to 1.9 ‰. TDS gradually decreased from 2460 to 1778 mg L-1. The values of TSS varied from 1.91 to 3.96 g L-1. Landfill leachate conductivity decreased from 4710 to 3408 μS cm-1. TDS, TSS, salinity, phosphorus concentration as well as the conductivity have been determined only for the case of landfill leachate at different flow rate and hydraulic retention time.

It is well known that the vegetation in the wetland systems play a significant role in purification process. Aquatic plants enhance nutrient removal through biomass accumulation, fixation of inorganic and organic particles and where ammonium-N is present, by the creation of an oxidized rhizosphere [93]. In the absence of plants, the gravel substrate provided significant wastewater treatment [94, 95], although most studies report improved nutrient removal where plants are present [96]. Our experiments without vegetation in the lab-scale subsurface vertical-flow wetland system leads to lower treatment efficiency in comparison whit that where in the laboratory system has grown vegetation (Fig. 18). That confirms the important role of the plants in purification process. On the other hand the lack of plants allows the use of additional organic carbon source, which achieves a denitrification process (Fig. 19). In these experiment was added methanol in the SSVFW without vegetation. As a result was observed decreasing of the nutrition elements and their elimination from the system.

**Figure 16.** Comparison of the [NH4

84 Applied Bioremediation - Active and Passive Approaches

and NO3 - +-N] and [NO3


The importance of nitrogen removal is comparable with that for organic carbon, toxic com‐ pounds and metals removal during the leachate treatment in SSVFW. Ammonium removal by nitrification in constructed wetlands differing in design and purpose was reported [89]. It is known that autotrophic nitrification consists of two successive aerobic reactions, the conver‐ sion of ammonium to nitrite by ammonium oxidizing bacteria and the conversion of nitrite to nitrate by nitrite oxidizing bacteria. The concentration of ammonium-nitrogen in the influent used in this study was relatively high. So, it was interesting to record the changes of NH4



+ -N

**Figure 18.** Treatment efficiency during the experiments with/without *Phragmites australis*

Nutrients and Organic Matter Removal in a Vertical-Flow Constructed Wetland

http://dx.doi.org/10.5772/56245

87

**Figure 19.** Nutrition concentration decreasing with applying of additional carbon source

**Figure 17.** Comparison of the [PO4 3-] values of the treated landfill leachate at different flow rates

Nutrients and Organic Matter Removal in a Vertical-Flow Constructed Wetland http://dx.doi.org/10.5772/56245 87

**Figure 18.** Treatment efficiency during the experiments with/without *Phragmites australis*

**Figure 19.** Nutrition concentration decreasing with applying of additional carbon source

**Figure 17.** Comparison of the [PO4

86 Applied Bioremediation - Active and Passive Approaches

3-] values of the treated landfill leachate at different flow rates

#### **6. Conclusions**

Activated sludge reactor, susbsurface vertical-flow wetland and hybrid installation were studied for aerobic treatment and polishing of two types wastewater - pig slurry and landfill leachate. It was established that the values of the treated water characteristics significantly decreased for comparatively short time accompanied by odour elimination and neutralization of wastewater. Significant COD and BOD decreasing were attained in those cases and the aquatic standards were met. Fully elimination of the ammonium-nitrogen in the SSVFW was achieved for longer period of time in comparison whit that in the ASR. Decreasing of obtained nitrate-nitrogen was not achieved in the SSVFW with growing *Phragmites australis* because of absence of anoxic conditions and probably of insufficient organic carbon source. In the SSVFW without vegetation was achieved denitrification process. It was established that the higher flow rate leads to longer period needed for treatment. The recirculation ratios also influence the purification process. Alternating between water movement through the SSVFW and stagnant periods resulted in a varying extent of purification, and the longer the stagnant period of the water in SSVFW the shorter the period for obtaining the desired characteristics of the effluent water was. These investigations show that the use of SSVFW is also effective as ASR and combination of the processes accelerate the purification process. The SSVFW has some advantages simulating the processes occurring in the natural wetlands, easy maintenance, energy conservation and cost effectiveness.

SSVFW – Subsurface Vertical Flow Wetland

Silviya Lavrova and Bogdana Koumanova\*

\*Address all correspondence to: bkk@uctm.edu

vironment Research (1992). , 64, 776-81.

Wetlands Team December; (2003).

ers, Boca Raton; (1993).

35, 215-221.

University of Chemical Technology and Metallurgy, Sofia, Bulgaria

[1] Reed, S, & Brown, D. Constructed Wetland Design- The First Generation, Water En‐

Nutrients and Organic Matter Removal in a Vertical-Flow Constructed Wetland

http://dx.doi.org/10.5772/56245

89

[2] Technical/Regulatory GuidelineTechnical and Regulatory Guidance Document for Constructed Treatment Wetlands. The Interstate Technology and Regulatory Council

[4] Moshiri, G. Constructed Wetlands for Water Quality Improvement. Lewis Publish‐

[5] Cooper, P, Smith, M, & Maynard, H. The Design and Performance of a Nitrifying Vertical Flow Reed Bed Treatment System. Water Science and Technology (1996). ,

[6] Haberl, R. Constructed Wetlands: A Chance to Solve Wastewater Problems in Devel‐

[7] Vymazal, J. Types of Constructed Wetlands for Wastewater Treatment: Their Poten‐ tial for Nutrient Removal, In: Vymazal J. (ed.) Transformations of Nutrients in Natu‐

[3] Kadlec, R, & Knihght, R. Treatment wetlands. Lewis Publishers; (1996).

oping Countries. Water Science and Technology (1999). , 40, 11-17.

ral and Constructed Wetlands. Backhuys Publishers; (2001). , 1-93.

TKN – Total Kjehldahl Nitrogen

TN – Total Nitrogen

VF – Vertical Flow

**Author details**

**References**

TP – Total Phosphorus

TSS – Total Suspended Solids

#### **Nomenclature**

AS - Activated Sludge

ASR - Aerobic Sludge Reactor

ASR-SSVFW - Aerobic Sludge Reactor - Subsurface Vertical-Flow Wetland (hybrid installa‐ tion)

BOD - Biochemical Oxygen Demand

COD – Chemical Oxygen Demand

CW – Constructed Wetland

DO – Dissolved Oxygen

LCA - Life Cycle Assessment

NH4 + -N – Ammonium Nitrogen

NO2 - -N – Nitrite Nitrogen

NO3 - -N – Nitrate Nitrogen

PO4 3- -P - Phosphates


**6. Conclusions**

88 Applied Bioremediation - Active and Passive Approaches

**Nomenclature**

tion)

NH4 +

NO2 -

NO3 -

PO4

AS - Activated Sludge

ASR - Aerobic Sludge Reactor

BOD - Biochemical Oxygen Demand

COD – Chemical Oxygen Demand

CW – Constructed Wetland

LCA - Life Cycle Assessment



3- -P - Phosphates


DO – Dissolved Oxygen

energy conservation and cost effectiveness.

Activated sludge reactor, susbsurface vertical-flow wetland and hybrid installation were studied for aerobic treatment and polishing of two types wastewater - pig slurry and landfill leachate. It was established that the values of the treated water characteristics significantly decreased for comparatively short time accompanied by odour elimination and neutralization of wastewater. Significant COD and BOD decreasing were attained in those cases and the aquatic standards were met. Fully elimination of the ammonium-nitrogen in the SSVFW was achieved for longer period of time in comparison whit that in the ASR. Decreasing of obtained nitrate-nitrogen was not achieved in the SSVFW with growing *Phragmites australis* because of absence of anoxic conditions and probably of insufficient organic carbon source. In the SSVFW without vegetation was achieved denitrification process. It was established that the higher flow rate leads to longer period needed for treatment. The recirculation ratios also influence the purification process. Alternating between water movement through the SSVFW and stagnant periods resulted in a varying extent of purification, and the longer the stagnant period of the water in SSVFW the shorter the period for obtaining the desired characteristics of the effluent water was. These investigations show that the use of SSVFW is also effective as ASR and combination of the processes accelerate the purification process. The SSVFW has some advantages simulating the processes occurring in the natural wetlands, easy maintenance,

ASR-SSVFW - Aerobic Sludge Reactor - Subsurface Vertical-Flow Wetland (hybrid installa‐

