a novel technology for treating municipal wastewater at demonstrative scale different hight

8/7/2019 A NOVEL TECHNOLOGY FOR TREATING MUNICIPAL WASTEWATER AT DEMONSTRATIVE SCALE different hight

http://slidepdf.com/reader/full/a-novel-technology-for-treating-municipal-wastewater-at-demonstrative-scale 1/6



IRSA has developed and applied successfully such a technology for treating, at laboratory scale,

municipal and industrial wastewater (Di Iaconi et al., 2006; Ramadori et al., 2006).

After such tests, a demonstrative unit was implemented with a grant of the European Commission by

LIFE financial instrument (project: life05 ENV/IT/000868; www.perbiof-europe.com). Therefore, a

demonstrative plant was designed and constructed with the cooperation of IRIDE SpA (a big Italian multi-

utility company) and Université de Savoie. This plant was fed with the primary effluent coming from the

municipal WWTP (200,000 p.e.) of Bari West, a town located in Apulia, a Southern Italy Region. The

present paper reports the results obtained during this experimental campaign.

Materials and Methods

Demonstrative SBBGR system and operation. The SBBGR prototype used during the present experimentation

consists of a cylindrical zinc plated steel reactor having a diameter and a height of 1 and 4 meters,

respectively.

part 2

part 1

part 3

Figure 1. Sketch and photo of SBBGR.

Looking at figure 1, which shows a sketch and photo of the prototype, it is possible to observe that the

SBBGR consists of 3 main parts:

- the lower part (i.e., part 1 in figure 1) distributes to part 2 the influent fed by volumetric pump and/or semi-

treated wastewater taken from part 3 by a recirculation pump;

- the central part (i.e., part 2) is the reactive zone as it contains the biomass. This element is filled with

biomass support material (KMT-k1 elements from Kaldness). The support is confined between two

surfaces of slabs with 18 disseminators in order to obtain a good distribution of the liquid and air in the

biomass zone. A window-type opening is provided on the upper surface for allowing biomass samples to

be taken for analysis;

- the higher part (i.e., part 3) acts as a storage tank in which aeration takes place. A volumetric pump takes

the oxygenated liquid from here to part 1 at a flow rate value of 2 m3

/h. The pump can extract the liquid at



two different levels as shown in figure 1. The aeration is performed by a blower connected with somediffusers (fine bubble disc system).

The SBBGR carries out a treatment cycle consisting of three consecutive phases: filling, reaction(under aerobic conditions) and drawing. In the filling phase, the wastewater to be treated is fed into part 1 of the plant. During this phase, the liquid passes through the bed (i.e. part 2) and then goes to part 3. When afirst, predetermined, liquid level in part 3 is reached, the recirculation pump and blower start. In theseconditions, the aerated wastewater reaches part 1, passes through the bed (i.e. part 2) together with rawwastewater and then reaches part 3 where it is aerated and recycled again. When a second, predetermined,liquid level in part 3 is reached, the filling pump stops while the liquid recirculation continues until the endof the reaction phase. Finally, the treated wastewater is drawn by a motorised valve located at the bottom of part 3 (see figure 1).The operative schedule (filling, recirculation, aeration, drawing, etc.) is completely automated, using a programmable logic controller (PLC) although the plant components can also be switched on or off manually. A pressure meter set at the bottom (i.e. part 1) of the reactor measures biofilter headlosses on-linedue to the biomass growth and captured suspended solids occurring in the wastewater during the operation of the reactor (i.e., working operation). When a fixed set value of head loss is reached, a washing step is carried

out by compressed air until the headloss is decreased down to a definite value. Washing water was collectedand measured (as TSS) in order to calculate the specific sludge production. During the experimental period,the air and liquid recirculation flow rates, 3 and 2 m

3/h, respectively, were controlled by flow meters whereas

the pH, which was continuously monitored, was always in the range 7.0-8.0.The SBBGR system was set up at a large municipal wastewater treatment plant (200,000 p.e.), located

in Southern Italy (Bari) and activated sludge from the plant was used as inoculumDuring the 3 month start-up period (i.e., period A), careful attention was paid to the generation of granular biomass. Specifically, taking into account the wastewater composition, the organic loading value was

progressively increased from 0.05 up to 0.5 kgCOD/m3⋅d by adjusting the wastewater volume fed to plant.

Once granulation had been achieved, the experimental activities continued in order to assess both granulestability and plant performance. In particular, during this period (i.e., period B) the plant hydraulic residencetime was progressively decreased from 12 to 3 h by increasing flow rate.

Wastewater composition. SBBGR was fed with the primary effluent coming from the municipal wastewater treatment plant of Bari. The composition of the SBBGR influent wastewater in the investigated period isreported in table 1:

Table 1. Average composition of municipal wastewater fed to SBBGR during the investigation period

Parameter Average value

COD [mg/L] 355

CODsol [mg/L] 200

TKN [mg/L] 45

NH4-N [mg/L] 33

NO3-N [mg/L] 1.5

pH 7.5

Chlorides [mg/L] 1,200

PO4-P [mg/L] 3

TSS [mg/L] 125

VSS [mg/L] 115



Analytical methods- COD (chemical oxygen demand), TKN (Kjeldahl nitrogen), NH4-N, NOx-N, PO4-P,TSS (total suspended solids) and VSS (volatile suspended solids) were determined according to StandardMethods (1999). Instantaneous and composite samples of influent and effluent were taken using automaticsamplers.

Results and Discussion

Biomass granulation was obtained towards the end of the start-up period. Throughout this period, thehydraulic loading was adjusted in order to obtain a progressive increase in organic loading from a minimum

of 0.05 kgCOD/m3⋅d up to maximum value of 0.5 kgCOD/m3

⋅d. In particular, during the first few days of thestart up period, it was observed that a thin biofilm completely covered the carrier surface. Later on, anincrease in biofilm thickness was recorded which therefore led to an increase in both biomass concentrationand headloss values. Subsequently, detachment of biomass particles was observed with deposition inside theinterstitial pores of the carrier (i.e., pores produced by packing). The particles entrapped inside the carrier still continued to grow reaching a size and shape similar to granules. At the end of the start-up period, the

headloss along the whole bed and the average biomass concentration were 3 m and 35 gTSS/L. The granuleswere the prevailing form of biomass present in the bed. In fact, specific quantitative measurements showedthat about 75% of biomass content in the bed was made of granules. Looking at figure 2, which shows a photo of biomass granules, it is possible to see that the maximum diameter of the granules was 4-5 mm

Figure 2. A photograph of the granules.

After the start-up period, the plant was operated for an additional eight months during which the

hydraulic residence time of the SBBGR was progressively decreased from 12 to 3 h by increasing hydraulicloading. Referring to this period (i.e., period B), figures 3 shows COD and TSS average concentrationsrecorded in the effluent of prototype as well as their relative removal efficiencies all as functions of hydraulicresidence time. Looking at this figure, it is possible to note that the COD concentration in the effluent of prototype was always lower than 60 mg/L with removal efficiencies higher than 85% independently of hydraulic residence time and influent COD value. Such a result can be ascribed to the great operationflexibility and stability of the SBBGR system towards volumetric flow rate and wastewater compositionchanges. Regarding TSS, the data in figure 3 show that the concentration of total suspended solids in treatedeffluent was lower than 30 mg/L with removal efficiencies higher than 80% independently of the hydraulicresidence time value and influent TSS value. Such good filtration performances can be ascribed to the low bed porosity values reached (i.e. lower than 0.15).



0

20

40

60

80

0 3 6 9 12Hydraulic residence time (h)

C O D e f f , T S S e f f ( m g / L )

0

20

40

60

80

100

CODeff

TSSeff

COD rem. eff. (%)

TSS rem. eff. (%) C O D a n d T S S r e m o v a l e f f i c i e

n c y ( % )

Figure 3. COD and TSS concentrations in the effluent and their relative removal efficiencies as functions of hydraulic residence

time during period B.

Referring to nitrogen, figure 4 reports, for the same period, TKN and oxidised nitrogen average

concentrations recorded in the effluent as well as TKN removal efficiency all as functions of hydraulic

residence time. Looking at this figure, it is possible to observe that the removal of TKN was always higher

than 80% independently of the hydraulic residence time value. Moreover, oxidised nitrogen (NOx-N)

concentration in the treated effluents was always lower than 5 mg/L. Considering that in the prototype

treatment cycle there was no planned anoxic phase, such a result indicates that in the plant simultaneous

denitrification occurred. This result can be ascribed to both high biomass concentration (around 40KgTSS/m3

bed) and transient conditions, as in such conditions oxygen cannot penetrate inside the deeper

layers of biomass and denitrifying bacteria can find carbon sources coming from storage or hydrolysis

products of particulate organic matter present in the feed.

0

10

20

30

40

0 3 6 9 12

Hydraulic residence time (h)

T K N e f f , N O x - N

e f f ( m g / L )

0

20

40

60

80

100

TKNeff NOx-Neff

TKN rem. eff. (%)

T K N r e m o v a l e f f i c i e n c y ( % )

Figure 4 TKN and NO x-N concentrations in the effluent and TKN removal efficiencies as functions of hydraulic residence timeduring period B.



During the whole experimental campaign a very low sludge production value (i.e, almost onemagnitude order lower than that commonly reported for conventional systems) was obtained. Such a lowvalue of sludge production can be explained considering the very high sludge age value ( θc≈150 d) of SBBGR that led to a biomass concentration as high as 40 gTSS/L bed

Conclusions

The main results obtained during the transfer on a demonstrative scale of aerobic granulation in aSBBGR system for treating municipal wastewater are as follows:

- granular biomass generation was obtained during the first 90 days of the experimental period;

- the SBBGR was characterised by satisfactory COD, nitrogen and total suspended solids removal

efficiencies (higher than 80%) throughout the experimental period. In addition, these efficiency removalswere almost independent of investigated hydraulic residence time (i.e., from 12 down to 3 h);

- the process was characterised by a very low sludge production (i.e., almost one magnitude order lower than that commonly reported for conventional systems).

References

Di Iaconi, C., Ramadori, R., Lopez, A., Passino, R. (2005a). Hydraulic shear stress calculation in a sequencing batch biofilm reactor with granular biomass. Environ. Sci. & Tech., 39(3), 889-894.

Di Iaconi, C., R. Ramadori and A., Lopez (2005b). Aerobic granulation during the start up period of a periodic biofilter. In: Aerobic Granular Sludge. S. Bathe, M. K. De Kreuk, B. S. Mc Swain and N. Schwarzenbeck. Water and Envir. Manag. Series (WEMS), London, UK, ISBN: 1843395096.

Di Iaconi, C., Ramadori, R., Lopez, A. (2006). Combined biological and chemical degradation for treating amature municipal leachate. Bioch. Eng. Journ., 31, 118-124.

Di Iaconi C., G. Del Moro, Lopez, A., Ramadori, R. (2007). The essential role of filling material in aerobicgranular biomass generation in a periodic submerged biofilter. Int. J. Env. Waste Man. (in press)

Ramadori, R., Di Iaconi, C., Lopez, A., Passino, R. (2006). An innovative technology based on aerobic granular biomass for treating municipal and/or industrial wastewater with low environmental impact. Wat. Sci. Tech.,53(12), 321-329.

Standard Methods for the Examination of Water and Wastewater (1999). 20th ed, American Public HealthAssociation/American Water Works Association/ Water Environment Federation, Washington DC, USA.

a novel technology for treating municipal wastewater at demonstrative scale different hight

Documents