LECA. One was planted (CWP) with common reeds. (Phragmites australis) and the other was kept unplanted as a control unit (CWC). The feeding CBW was.
Treatment of cork processing industrial effluent with an innovative system of Constructed Wetland and Ozonation Diana Santos (1), Williams Silva(1), Arlindo Gomes (1), Rogério Simões (1), Roberto Pascoa (1), António Albuquerque (2) and Alexandros Stefanakis (3) (1)
Unity of Textile & Paper Materials and Department of Chemistry, University of Beira Interior, Covilhã - Portugal; (2)
Department of Civil Engineering and Architecture, University of Beira Interior, Covilhã – Portugal; (3)
Department of Environmental Engineering, Democritus University of Thrace, Greece;
Abstract The performance of two constructed wetlands (CWs) with horizontal subsurface flow (HSSF) configuration was investigated during a three phases treatment of cork boiling wastewater (CBW). The two CWs were filled with LECA. One was planted (CWP) with common reeds (Phragmites australis) and the other was kept unplanted as a control unit (CWC). The feeding CBW was sequentially diluted to 500, 600 and 750 mg/L COD and pH was set to 6.5-7.5. Other features of the feed solution were the intense dark colour, total phenols (TPh) concentration ranging from 36 to 62 mg/L and low biodegradability. Both CW units showed similar COD (44.7 and 56.6%, respectively) and TPh (40 and 65%, respectively) removal rates for a working period of 4 months. First results indicate that the presence of plants improved the system performance only in terms of total phosphorus (TP) removal (33% and 9% in the CWL and CWC unit, respectively). After phase 1 (500 mg/L influent COD) the major drawback was the absence of decolourization which was close to null or negative. To increase decolourization, ozonation was implemented as a post-treatment stage. However, the amount of ozone used was limited to 18.9±2.3 mg to keep the cost low. Despite the limited mean yield of 27%, it was possible to achieve colour removal above 85% and increase the biodegradability from 390 to 955%. These are important facts towards the pollution elimination and may consequently contribute to sustainable use of industrial water.
Introduction The Water Framework Directive issued by the EU compels industries to the sustainable use of water. This objective requires the reduction of water consumption and of the polluted water to ensure that future generations will have equal opportunities for economic and social development. The production of cork stoppers is the most valuable outcome of the cork industry. Therefore, the economic sustainability of the cork production is closely dependent on public preference for cork stoppers in detriment of synthetic materials. The first stage of the cork industrial process is focused on the cleaning, disinfection and
moistening of the raw material. For this purpose, the corkwood is immersed in boiling water up to one hour after dried in open air [1,2]. The amount of water used varies between 0.35 to 0.70 m³/tn, and depends on the water reuse percentage, which is limited from 3 to 6 times in the case of cork used for stoppers production. It is necessary to ensure the absence of organic contaminants, namely the 2,4,6-trichloroanisole (TCA), which may cause the spoilage of more than 80% of wine bottles during the storage. Therefore, the presence of TCA in stoppers is exhaustibly controlled by methods with detection limits between 1 and 2 ng/g and determines the possibility of its usage to seal wine bottles [3]. Cork boiling wastewater (CBW) has a dark colour and contains some corkwood extracts such as phenolic acids and tannic compounds [2]. Biological treatment is difficult to be implemented due to the high concentration of bio-recalcitrant compounds, some of them also contribute to the high effluent acute toxicity (4.1 to 12.3 toxic units, TU) [4]. The Total Phenols (TPh) content is reported to be between 1.0 and 3.5 g of gallic acid/L. The effluent COD (Chemical Oxygen Demand) varies from 1300 to 4400 mg/L and the BOD5 (Biological Oxygen Demand) is between 875 and 1800 mg/L, which corresponds to a biodegradability index (BI) (BOD5 /COD ratio) below the recommended limit of 0.40 for the adoption of conventional biological treatment processes [1,2,4,5]. Adaptation of the Constructed Wetland (CW) technology meets increasing worldwide interest compared to conventional systems, namely for domestic and municipal wastewater treatment, as also for industrial wastewater such as textiles, food processing and winery industries. It appears as a sustainable alternative to fulfill the requirements of a respective biological treatment [6]. CWs offer a series of ecological, economical and engineering benefits, including high nutrient absorption capacity, simplicity, process stability, no sludge production, reduced construction, operation and maintenance costs and creation of a wildlife habitat, which allow for resource conservation and environmental protection [6]. In addition, CWs show good effectiveness in the removal of organic matter (up to 80% for COD), total phosphorus (TP), total nitrogen, etc. [6,7]. Among the several possible configurations for the CW systems the most common in Portugal and in mos t European and
Mediterranean countries are the horizontal subsurface flow (HSSF) systems used for BOD5 and suspended solids removal from wastewater [6]. Systems with subsurface flow promote the passage of the wastewater through a porous media in which aquatic plants are growing. They have a high tolerance even in cold climates, and practically no odour and mosquito appearance. The transformations and removal of influent pollutants occur through a series of chemical (redox, precipitation), physical (filtration, sedimentation, adsorption) and biological (biodegradation, nitrification) processes [6-8]. The substrate media promotes plant fixation and the development of the biofilm. Clogging problems used to be a problem but today are not very extended. Although clogging mechanisms are not yet very well understood, it is known that suspended solids accumulation, biomass growth, chemical precipitation and rhizomes and roots development are the main mechanisms [7,9]. Lightexpanded clay aggregate (LECA) has been used as an alternative substrate media to prevent clogging and increase the treatment capacity. It possesses high porosity and specific surface area, which allows for a good biofilm adhesion and a high hydraulic conductivity [9]. Phragmites australis is a perennial plant species most commonly used in CWs, with an extensive system of rhizomes [6,9]. This species presents a vegetative cycle that begins in the first spring months, when the shoots development shows a high growth rate. In summer the plants reach the peak of their growth (height over 2 m). The first signs of aging usually appear in autumn, and the progressive drying of the leaves and shoots can be observed during the following months , until the beginning of the next growing season [9]. Due to strict environmental regulations it is difficult to achieve the quality requirements either for effluent discharge or water reuse in the case of industrial wastewater using only CWs [6,9]. Thus, when effluents have toxic non-biodegradable pollutants the operation with partial effluent recirculation or a post-treatment stage may be necessary to comply with legislation requirements [10]. Two HSSF CW systems filled with LECA, one planted and one unplanted, were fed with diluted CBW (COD concentration of 500, 600 and 750 mg/L). System monitoring showed that colour removal in both units was only 4.5 and 23.9%, while in some cases the effluent colour increased. Thus, ozonation was tested as a posttreatment phase. Chemical oxidation techniques are increasingly used as pre- or post-treatment of industrial effluents. In the first case, they can be applied to raw wastewater or membrane concentrates to reduce macromolecule molecular weight, increase biodegradability and reduce the toxicity, allowing for the viability of subsequent biological treatment. In the other case, they are used to deliver high
quality water appropriate for reuse or discharge [11]. One widely used procedure is ozonation, especially when hazardous and bio-recalcitrant organic and inorganic compounds are present. The powerful oxidizing capabilities of ozone and the absence of hazardous decomposition products make this a potentially useful post-treatment agent, especially when decolourization is required, like in the case of textile effluents [11]. The aim of this work is to conduct a preliminary investigation of the potential for cork processing industry effluent quality improvement with the use of an innovative combined treatment system of CWs and ozonation.
Materials and Methods Constructed wetland systems Two HSSF CW laboratory-scale units were used: one planted with Phragmites australis (CWP) and one unplanted as a control unit (CWC). CWP dimensions are 34.8 cm x 15.0 cm (length x width), with a total surface area of 522 cm² (Fig. 1a). Respective values for CWC were 29.7 cm x 10.0 cm and 297 cm² (Fig. 1b) . Both units contained LECA as substrate media (porosity 38.33%). LECA depth in CWP and CWC units was 14.3 and 13 cm, respectively. Water depth was 9.8 cm in both units. The influent flow rate was adjusted to 9 and 16 ml/h for the CWC and CWP, respectively. The hydraulic retention time (HRT) applied in both units was 5 days.
(a)
(b)
Figure 1. Schematic representation of (a) planted CWP unit and (b) unplanted CWC unit. Biomass The biomass used as inoculum in these experiments was collected from the aeration tank of a Wastewater Treatment Plant based on activated sludge process for domestic wastewater treatment. After the collection, the biomass was kept under vigorous aeration and fed with a solution containing glucose and acetate with balanced composition of the C:N:P ratio (100:5:1). Plants and start-up period
Post treatment Ozonation was applied as a final effluent polishing stage of both CW systems. A Fischer Model 502 ozone generator (Germany) was used to produce ozone gas from dry pure oxygen. The oxidation of CW effluents was conducted in a closed vessel of 500 mL with mechanical stirrer to promote the ozone gas transfer to the solution. The ozonation lasted 10 min and corresponded to the application of 18.9 ± 2.3 mg of ozone. The yield calculation for the oxidation was based on the difference between the initial ozone production rate (mg/min) and the amount of ozone exiting the unit and fixed in KI. All determinations were performed by the iodometric method. Ozonation was applied during phases 2 and 3.
Results and Discussion
Stage 1
The characteristics of feed solutions and the performance of both CWs are presented in Table 1.
Stage 2
Wastewater The full operating period started with the feeding of CBW solutions of 500 mg/L COD (Phase 1). Then the organic load increased to 600 mg/L COD (Phase 2) and finally it reached 750 mg/L COD (Phase 3). Each phase lasted for 20, 18 and 33 days, respectively. Operating conditions did not change until the achievement of steady COD and TPh removal rates. Both CWs were placed indoors. Room temperature showed significant variation between May and November (35 and 14°C, respectively). Feed solutions were kept at 4°C to avoid biological degradation and pH was adjusted to 6.5 – 7.5.
temperature were carried out with a pH meter (713 pH meter, Metrohm) and a temperature sensor (VWR).
Stage 3
Common reeds (Phragmites australis) were established in May 2012 and the unit operation started. During the first 4 weeks both units were fed with synthetic wastewater with an organic load of 300 mg/L COD (acetate) before the application of CBW.
Influent CWP Effluent CWC Effluent Influent CWP Effluent CWC Effluent Influent CWP Effluent CWC Effluent
COD
TOC
BOD
BI
TPh
550,9
219,5
148,9
0,29
36
A254 nm 0,125
56,6±5,2
63,3
61,1
0,21
65±1,7
20±28
55,7±8,6
60,7
35,7
0,29
64,6±3,3
25,6±18,4
628,7
352,9
74,7
0,12
47,8
0,238
52,1±8
68,2±6,3 71,7±17,8
0,04
56,5±13,6 42,02±19,75
55,8±8,9
74,9±5,7 77,7±13,3
0,03
57,5±12,4 50,84±20,17
750
330
168,3
0,13
61,9
0,252
44,7±14,7 37,0±2,6 77,8±17,1 0,06±0,02
40,2±8,3
37,3±15,5
53,6±10,8 48,8±8,0 84,1±18,1 0,06±0,02
47,0±8,0
41,1±13,6
Table 1. Characteristics of the CBW solutions used during the three operational phases and respective percentage removal rates for CWP and CWC units. (Influent; mg/L and effluent; percentage, mean value ± standard deviation).
Experimental procedure Weekly samples were taken from the CWP and CWC beds at three points: influent, ½ of unit length and effluent to determine pH, COD, BOD5 , TP, TPh, colour (absorbance at 580 nm – A580nm) and aromatic compounds (absorbance at 254 nm – A254 nm). CWP and CWC effluent samples were kept at 4°C. Analytical determinations were performed in triplicates. The HRT of CWs was fortnightly monitored.
Despite the dilutions of CBW (from 1:4 to 1:2) in order to modify the COD concentration for each treatment phase, the BI values ranged only from 0.12 to 0.27, which implies the presence of bio-recalcitrant organics. It is also interesting that both CWs presented similar removal rates for organic matter, TPh and aromatics, which varied for COD from 44.7 to 56.6% for an extended operational period (from 19 July to 5 November). During this period, mean temperature values were 34.5°C in August and 14°C in November. As temperature decreased, reed leaves started to dry in October. This was accompanied by a decrease in TP uptake by plants, since TP removal in the CWP unit decreased from 32.6 % in phase 2 to 22.1 % in phase 3, higher enough, however, compared to the unplanted CWC unit (maximum 8.6%). Moreover, results obtained during phase 1 implied that decolourization is the major issue for the system performance. Therefore, in phases 2 and 3 ozonation was tested as post-treatment.
Analytical methods COD, BOD5 and TOC were determined according to Standard Methods [12]. TPh was determined with the Folin-Ciocalteu reagent according to the method of Ainsworth and Gilliespie and expressed in terms of tannic acid mg/L [13]. TP concentration was measured using the cuvette tests LCK 350, following the DIN 38405 D11-4 procedure, and a Hach-Lange CADAS 50 spectrometer (Germany). The sample absorbance was determined at 254 and 580 nm, which represent the aromatic-compound content and the colour of the solution, respectively. Before absorbance measurements, samples were diluted at the rates of 1:50 and 1:10 for aromatics and colour determinations, respectively. Measurements of pH and
The results achieved by ozonation of the CW effluents are presented in Table 2. Despite the small amount of ozone applied (18.9±2.3 mg), chemical oxidation allowed for a decolourization ranging from 80 to 94%, which is not dependent on the CW effluent COD. The concentration of the major class of organic pollutants, the phenolic compounds, was also reduced up to 73%, which may also contribute to the detoxification (data not yet available) and to the increase of the BI. The results show a BOD5 enhancement of 526 and 720% for CWC and CWP, respectively, in phase 2 and 307 and 206% in phase 3, probably due to the increase of the available organic matter for bio-degradation as the COD removals were decreased in phases 2 and 3.
CWC
Stage 2
CWP
Variation (%) 1 Before After
CWC 2
CWP
Stage 3
2
Before After
COD 335 271
BOD 12 62
BI 0,03 0,23
TPh 31,2 8,3
A580nm 0,065 0,004
(-) 24
(+) 526
(+) 689
(-) 7,3
(-) 94
372 280
9 62
0,02 0,22
31,2 11,4
0,065 0,008
(-) 25 Variation (%) 1 Before 492,2±98,5 After 272,3±44,7
(+) 720
(+) 955
(-) 6,3
(-) 88
22,3±2,7 67,6±7,9
0,06±0,02 0,20±0,04
37,1±3,6 11,2±4,0
0,060±0,006 0,009±0,003
Variation (%) 1 (-) 44,3±6,3 (+) 307±53 (+) 437±32 (-) 69,6±4,0 (-) 85,3±3,7 Before 535,0±71,4 33,0±6,0 0,06±0,01 41,2±3,7 0,072±0,003 After 332,1±28,3 68,3±18,1 0,25±0,02 13,0±0,6 0,015±0,003 Variation (%) 1 (-) 37,6±3,7 (+) 206±27 (+) 390±182 (-) 68,2±1,9 (-) 79,6±4,7
Table 2. Results achieved by ozonation of the CW effluents. Units expressed as mg/L except for BI (dimensionless) and colour (A580nm); (1)(+) indicate increase and (-) indicate removal; (2)mean±standard deviation of three samples. Due to the small ozone yield (27%) applied, the CW effluent quality of both CWs is not within the limits for discharge or reuse, since COD concentration remains above 150 mg/L.
chloroanisoles and chlorophenols from contaminated cork samples”, J. of Chromatography A, 1122, 215, 2006. [4] Mendonça, E., Pereira, P., Martins, and Anselmo, A.M., “Fungal Biodegradation and Detoxification of Cork Boiling wastewaters” Eng. Life Sci, 4, 144, 2004. [5] Bernardo, M., Santos, A., Cantinho, P., and Minhalma, M., “Cork industry wastewater partition by UF/NF: A biodegradation and valorisation study”, Water Res., 45, 904, 2011. [6] Davis, L., “A handbook of constructed wetlands”, volume 1, General Considerations, USEPA Region III with USDA, NRCS, 1995. [7] Soon-An Ong, Uchiyama, K., Inadama, D., and Yamagiwa, K., “Simultaneous removal of color, organic compounds and nutrients in azo dye-containing wastewater using up-flow constructed wetland”, J. of Hazard. Materials, 165, 696, 2009. [8] Vymazal, J. (2007). Removal of nutrients various types of constructed wetlands, Sci. Total Environ. 380, 48–65
in
Conclusions Despite the small amount of ozone applied as posttreatment and the low reaction yield, the viability of this option to achieve significant removal of colour (79.6 to 94.0%) and TPh (63 to 73%) was demonstrated. The increase of BOD5 and consequently of the BI should be noticed and could also contribute to the reduction of effluent toxicity and, thus, of the environmental impact of the cork industry effluent. However, the total performance of the integrated system is not yet appropriate for effluent discharge to natural watercourses or reuse, as COD remains above the limit of 150 mg/L. Therefore, CW performance needs further improvement, which could be achieved as the maturity of the system proceeds with time and through further modification of the system setup.
[9] Albuquerque, A., Oliveira, J., Semitela, S., and Amaral, L., “Evaluation of the effectiveness of horizontal subsurface flow constructed wetlands for different media” J. of Envir. Sciences, 22, 820, 2010.
Future work includes the performance evaluation of the integrated system for wastewater detoxification and comparison of the ozonation results as post-treatment and as pre-treatment for the same limited amount of oxidant and organic load.
[12] APHA, AWWA and FEW, “Standard Methods for the Examination of Water and Wastewater”, 20th Ed., Washington, DC, USA, 1998.
References [1] Greeves, A.J., Churchey, J.H., Hutching, M.G., Philips, D.A.S., and Taylor, J.A., “Ozonation kinetics of cork-processing water in a bubble column reactor”, Water Res., 42, 2473, 2008. [2] Benitez, F.J., Acero, J.L., and Leal, A.I., “Application of MF and UF processes to cork processing wastewaters and assessment of membrane fouling”, Sep. And Purif. Technol., 50, 354, 206. [3] Insa, S., Salvadó, V., and Anticó, E., “Assays on the simultaneous determination and elimination of
[10] Alexandros I. Stefanakis and Vassilios A. Tsihrintzis . Effect of Outlet Water Level Raising and Effluent Recirculation on Removal Efficiency of Pilot-scale, Horizontal Subsurface Flow Constructed Wetlands. Desalination 248 (1-3), 961 – 976, 2009. [11] Woodard, F., “Industrial Wastewater Treatment Handbook”, Butterwort Heinemann Ed., USA, 2nd Ed., 2001.
[13] Ainsworth E.A. and Gillespie K.M., “Estimation of total phenolic content and other oxidation substrates in plant tissues using Folin-Ciocalteu reagent”, Nat. Protoc, 2, 857, 2007. Acknowledgements Thanks are due to FCT and FEDER for funding the Project (PTDC/AGR-AAM/102042/2008) and Diana Santos also thanks FCT and FEDER for their Masters grants.
