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Zero Energy Sewage Treatment Plants

GHEORGHE BADEA, DAN MUREŞAN, IOAN AŞCHILEAN, EMIL MOLDOVAN, FLORIN BADEA, CĂLIN VAC

Building Services Engineering Department, Technical University of Cluj-Napoca

Boulevard December 21, no. 128-130, 400604, Cluj-Napoca ROMÂNIA

[email protected] http://instalatii.utcluj.ro/departamente.php Abstract: It is now obvious that the 20th century was the time of the greatest technological discoveries, generating radical transformations of human civilization, with complex and unexpected effects on the lives of the planet's inhabitants. Until not so long ago, the planet's natural resources had been considered sufficient for satisfying the needs of humanity. The population boom and the unprecedented development in all fields of activity have created an increased demand of raw materials and energy, highlighting serious ecological imbalances. In this context the collection and treatment of wastewater represents an important component for environmental protection, distinctively underlined during the 1992 United Nations Conference on Environment and Development in Rio de Janeiro and later during the 2002 World Summit on Sustainable Development in Johannesburg. This paper presents sustainable zero energy sewage treatment solutions, using extensive treatment processes, based on natural decomposition and assimilation phenomena. The system consists of the multifunctional filtering anaerobic biological reactor representing the primary step, the lower flow horizontal plate filter representing the secondary step and the upper flow horizontal plate filter representing the tertiary step. Key words – environmental protection, specific influent flow, collection system, treatment system, local communities. 1 Introduction The sustainable collection and treatment of sewage is a highly important technological problem for all human communities due to the fact that avoiding environmental pollution, and pollution of surface water respectively, must equally concern all the members of local communities. Thus, in order for a wastewater collection and treatment system to be sustainable, it must aim to fulfil several efficiency and performance criteria, such as: • ensuring the health and hygiene of its users and

not only; • protecting the environment and the directly or

indirectly affected natural resources needed to build and operate these systems;

• providing highly efficient robust technologies, flexibility and adaptability, which allow for easy implementation in any conditions;

• providing economically optimum solutions, which allow access to a source of financing for building them, but also the generation of reasonable operational costs, which can be supported by users;

• providing solutions which can be accepted by institutions by respecting the technological and

legal framework, as well as fitting them into the social and cultural framework created by their users.

2 Problem Formulation In engineering practice there are usually two large categories of treatment plants: plants that use intensive treatment processes (see fig.1) and plants that use extensive treatment processes (see fig.2). In principle a treatment plant consists of the procedures and process flows needed to eliminate pollutants from influent flows and is structured into three operational steps: the primary, secondary and tertiary steps, all of these followed more often than not by a complementary disinfection process.

Fig.1 Treatment plant using intensive processes

Computer Applications in Environmental Sciences and Renewable Energy

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Fig. 2 Treatment plant using extensive processes The notation used in the above figures have the following meanings: 1 - mechanical grill; 2 - sand/grease trap; 3 - primary decanter; 4 - activated sludge digester; 5 - secondary decanter; 6 - denitrification tank; 7 - filtering tank; 8 - disinfection tank. 9 – extensive process tank. Table 1 Treatment steps in the case of intensive and

extensive processes

No.

Trea

tmen

t ste

p

Intensive treatment step

Extensive treatment step

Equipment

Proc

edur

es

Equipment

Proc

edur

es

1

Prim

ary

Thin grills

Phys

ical

Anaerobic digester

Phys

ical

N

atur

al b

ioch

emic

al

Thick grills Anaerobic biological reactor

Sand/Grease trap Filtering

anaerobic biological reactor

Rotating sieves Multifunctional biological reactor Primary decanter

2

Seco

ndar

y

Activated sludge digester

Che

mic

al b

iolo

gica

l Lower flow horizontal plate

filter

Nat

ural

bio

chem

ical

Rotating biodiscs Percolator filters

Vertical plate filter

Membrane filters Upper flow plate

filter Secondary decanter

3

Terti

ary

Nitrification/denitrification in

activated sludge digesters

Bio

logi

cal

Che

mic

al

Nitrification/denitrification in plate

filters

Bio

chem

ical

na

tura

l

Chemical precipitation

Ammonia stripping

4

Dis

infe

ctio

n Hypochlorite dosing

Che

mic

al

Shallow biological lagoon N

atur

al

bioc

hem

ical

Ultraviolet

It is worth noticing that both the intensive and the extensive process contribute to the elimination of pollutants in wastewater; physical, chemical and biochemical processes are present in both versions, with the efficiency being influenced by their duration, intensity and succession (see table 1). Today the intensive processes are implemented on a large scale and are used for the treatment of sewage, regardless of the size of the influent flows or of their pollutant load quantities. The intensive treatment plants are sized (see table 2) on the basis of the influent flow, determined according to the specific return flow in the sewage network, which varies in developing countries from 30 l/c/day to 225 l/c/day [5] and in Central and Eastern Europe from 50 l/c/day to 320 l/c/day [1]. In Romania from 80 l/c/day to 150 l/c/day [2] and specific pollutant loads according to technical regulations [3], the parameters of the effluent flow must be according to the European [4] and national technical regulations [6]. Table 2 Treatment plant sizing parameters imposed

through technical regulations

No. Indicator – parameter U.M.

Values according

to NTPA

002/ 2005

Values according

to 98/15/EC

1 MTS mg/l 350 60 35

2 CBO5 mg O2/l 300 20 25

3 CCO – Cr mg O2/l 500 125 70

4 N – NH4 mg/l 30 2 3

5 PT mg/l 5 1 2

6 Specific return flow in the sewage network 80 - 150 l/c/day

Treatment plants that use intensive processes generally have higher investment costs and important operational energy consumption compared to the ones that use extensive processes (see table 3), which feature a series of natural decomposition and assimilation processes, with extremely low energy consumption. Today the extensive wastewater treatment solutions are known worldwide and are implemented individually, highlighting the advantages and disadvantages of each solution, without achieving a complete treatment of the influent flows, this being their most significant disadvantage.


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Table 3 Energy consumption for intensive and extensive treatment plants [7]

Type of unit Energy use for operation (kW•h/m3)

Extensive treatment plant with upper flow plate filter < 0.1

Extensive treatment plant with lower flow plate filter < 0.1

Extensive treatment plant with shallow biological

lagoon 0.11

Intensive treatment plant with continuous flow

activated sludge digester 0.73

Intensive treatment plant with discontinuous flow activated sludge digester

1.11

The anaerobic digester or the filtering anaerobic biological reactor ensures the elimination of total solids by 60 - 80%, while for the biochemical oxygen consumption and for the chemical oxygen consumption there are efficiencies of 50 - 85%, according to the hydraulic retention time, which can vary depending on the number of compartments from 2 - 4 hours to 24 - 72 hours [8, 9]. Their disadvantage is represented by the high volumes resulting due to the long hydraulic retention time needed when obtaining high efficiencies; moreover, the specific treatment processes do not allow the elimination of nitrogen and phosphorus. The bottom or upper flow plate filters show high efficiencies in the case of removing the consumption of biochemical and chemical oxygen, between 80 and 99%, and of total solids of up to 90%, but also of nitrogen of up to 40% [10]. The phosphorus can be removed between 45% and 85%, depending on the characteristics of the adopted filtering mass and the adopted method of operation [10, 5]. In the case of lower flow plate filters the disadvantage is represented by the clogging of the filtering mass with the total solids in the influent flows, requiring the change of the filtering mass in order to keep the efficiency of the treatment. In the case of upper flow plate filters, the total solids form deposits that lower the useful water volume for the treatment, requiring expensive cleaning or even relocation operations. Implementing these extensive technological solutions on a large scale is lacking at the moment due to the fact that, individually, they do not satisfy the performance requirements for the elimination of all pollutants, imposing the building of a treatment system which, sized on the basis of specific flows

and regulated loads (see table 2), requires large land areas, which are hard to identify and allocate by local authorities. Thus, for a specific return flow of 150 l/c/day and for rated influent flow loads [2], a 5,000 m2 area is needed for 1,000 inhabitants, determined according to the empirical sizing coefficients of 3 to 8 m2/capita [10] in the case of lower flow plate filters. 3 Problem solution In order to have an overall picture of the situations in which the extensive treatment solutions can be successfully implemented, a series of studies and experimental measurements have been conducted, which have highlighted significant differences between the influent flows parameters imposed by technical regulations for the sizing of treatment plants, compared to the parameters actually measured. Thus, in the case of the specific return flow in the sewage network imposed by the technical regulations, of 150 l/c/day, the experimental measurements and case studies have shown a return flow between 27.77 l/c/day and 68.98 l/c/day, in the case of individual homes placed in a small rural area [11]. In the case of a small settlement of 950 inhabitants, the experimental measurements (see table 5) have shown pollutant load values of influent flows much lower than the ones regulated by the technical regulations (see table 2); individual loads are presented synthetically in table 4. In order to highlight the variable nature of pollutant loads even more clearly, measurements have been in the case of influent flows for a settlement of 300,000 inhabitants (see table 6), determining, even in this case, values under the ones regulated by the technical regulations (see table 2).

Table 4 Influent pollutant flow loads for a settlement of 950 inhabitants

No. Name

Pollutant loads for the treatment plant with 950

inhabitants

Loads imposed by

the Romanian technical

regulations

1 MTS g/LE day 17 70

2 CCO gO2/LE day 23.1 120

3 CBO gO2/LE day 9.17 60

4 N g/LE day 3.26 11 5 P g/LE day 0.39 4


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Table 5 Influent flow loads for a settlement of 950 inhabitants

Name/ Period

MT

S

CC

O

CB

O

N

P

Flow

mg/

l

mgO

/l

mgO

/l

mg/

l

mg/

l

l/s

1 2 3 4 5 6 7

January 135 180 60.81 32.50 2.90 0.62

February 145 165 45 33.50 3.74 0.67 March 164 178 89.20 28.50 3.21 0,63 April 150 195 82.50 33.50 3.14 0.50 May 135 210 85.50 27.50 2.74 1.29 June 145 236 77.25 19.50 3.09 1.60

July 165 188 75.50 22.50 3.50 1.59 August 135 220 78.50 27.50 3.74 1.55

September 135 175 82.50 21.50 4.14 1.48 October 135 240 110 38.50 2.82 2.09

November 148 185 74.24 23.50 3.09 1.64 December 165 215 86.50 28.50 3.74 1.66

Average 2012

146.40

198.90 78.96 28.08 3.32 1.28

In this context, it is obvious that the extensive treatment solutions can benefit from a large-scale implementation, imposing the performance of on-site measurements as a preliminary phase before the planning stage, precisely as a result of the large fluctuations of influent flows and pollutant loads.

Table 6 Influent flow load variations for a settlement of 300,000 inhabitants

Name/ Period

MTS CCO CBO N P

mg/l mgO/l mgO/l mg/l mg/l

1 2 3 4 5 6 January 131 255.61 91.92 36.1 4.43

February 84 235.92 75.97 30.5 3.26 March 151 335 107.56 33.5 3.9 April 80 192.93 79.68 27.5 2.6 May 78 175.76 92.14 26.9 3.03 June 125 180.53 58.52 26.8 3.21 July 104 182.31 68.7 28.3 3.26

August 82 170.08 74.66 22.9 2.96 September 90 182.31 90 31.2 3.53

October 89 245.63 89 35.3 3.39 November 85 229.62 91.23 30.7 3.64 December 130 221.69 91.12 30.2 2.9

2012 average 102.58 217.53 84.54 30.41 3.84

Thus, the extensive treatment solutions can be implemented in many situations, finding a place in supplementing the treatment processes of existing plants, by providing them in the completion of biological steps [13], in building tertiary steps [12], and in treating sludges [14], as well as in building new sustainable treatment systems sued to satisfy the needs of an individual home, up to suburban or rural settlements, even more so as the extensive processes allow for the building of zero energy treatment systems, structured on the basis of the gravitational flow principle [15] proposed in this paper. 3.1 Zero energy treatment plant drawing A treatment plant using zero energy extensive natural technologies (see fig. 3) consists of a primary step identified by physical sedimentation processes and anaerobic biochemical processes taking place in multifunctional anaerobic filtering biological reactors (MAFBR), a secondary step identified by biochemical processes taking place in lower flow horizontal plate filters (LHPF) and a tertiary step (advanced) identified by upper flow plate filters (UPF), the disinfection taking place by means of shallow biological lagoons (BL).

Fig. 3 Treatment plant using extensive processes

The primary mechanical step consists of the multifunctional anaerobic filtering biological reactor (see fig. 4), with four large compartments, each having a series of subcompartments. The first compartment is made up of two compartments, the first subcompartment usually takes up 2/3 of the total tank volume, thus ensuring enough space for the sedimentation of total solids as sludge, as well as for the formation of the crust, with a height varying between 30 and 50 cm. The second compartment is made up of three subcompartments. In the subcompartments of the anaerobic biological reactor, the influent is directed downwards, passing under the semi-submerged walls or through the


ISBN: 978-960-474-370-4 122

descending pipes positioned on the partition walls. The flow direction of the influent is upwards, thus ensuring intense contact between the influent and the existing activated sludge.

Fig. 4 Functional partitioning of the multifunctional

anaerobic filtering biological reactor (MAFBR)

1 - flow straightener; 2 - foundation plate; 3 - vertical wall; 4 - closing plate; 5 - access lid; 6 - passing opening; 7 - submerged wall; 8 - influent inlet pipe; 9 - effluent outlet pipe; 10 - distribution chamber; 10' - collection chamber; 11 - deflector wall.

The third compartment is made up of three subcompartments. In the subcompartments of the filtering anaerobic reactor, the influent is directed upwards passing under the semi-submerged walls or through the descending pipes placed on the partition walls and then through the perforated foundation slab, making intense contact with the bacteria mass fixed on the biological support (filtering mass). The last compartment accomplishes the final clearing and settling stage, ensuring the passage towards the biological treatment step. The multifunctional anaerobic filtering biological reactor can be used for treating wastewater with various compositions. The treatment efficiency is 70 - 90% for (CCO) and 75 - 95% for (CBO5). The hydraulic retention time (HRT) is of 2 - 4 h for the first compartment, 16 - 24 h for the second compartment and 24 - 48 h for the third compartment, the evacuations times for the mineralised sludge is between 1 and 3 years and the operational priming time is three months. The hydraulic organic loading is between 65 and 150 g (CBO)/m3-day. The efficiency of the multifunctional anaerobic filtering biological reactor increases with the rise of the organic loading, having the capacity to take high loading variations for short periods of time. The accumulate sludge volume is 4 l/g (CBO5) for the first compartment and 1.4 l/g (CBO5) eliminated for the other compartments.

The secondary biological step and the tertiary advanced step are formed with the aid of plate filters (see fig. 5) positioned in various serial or parallel matrices. Plate filters are divided into two large categories: • upper flow plate filters; • lower flow plate filters.

Fig. 5. Classification of plate filters The upper flow plate filters are completely covered by water and have floating emergent or submergent vegetable mass in their composition. Depending on the local configuration and soil conditions, the upper flow plate filters can be built as terraces or dams, using the geodesy of the existing lands as much as possible, or as rectangular concrete shapes. As the wastewater flows and enters the upper flow plate filter, it is treated through sedimentation, filtration, oxidation, reduction and absorption processes. The lower flow horizontal plate filters consist of a layer of gravel representing the filtering mass, which can be vegetated or non-vegetated. The wastewater travels under/through the filtering mass, in permanent contact with the roots of the vegetable mass. The water level is controlled by an adjustable pipe system. A compulsory condition for their operation is that the height of the roots of the emergent vegetable mass must be lower by at least a third of the total height of the filtering mass in order to avoid favouring the emergence of anaerobic conditions. The organic loading of the sewage is removed by the bacterial mass and by the litter formed in/on the surface of the filtering mass and by the roots of the vegetable mass. The amount of oxygen that penetrates the filtering mass has an important role in the efficiency of the treatment. Due to the fact that the waste water level is lower than the upper part of


ISBN: 978-960-474-370-4 123

the vegetable mass during the treatment process, the risk associated with human or animal exposure to pathogenic organisms is minimised, and a correct operation does not offer habitable conditions for mosquitoes. The vertical flow plate filters are plate filters, which consist of a layer of gravel, representing the vegetated or non-vegetated filtering mass. The wastewater is distributed under pressure on the surface of the filtering mass by percolator pipes.

The water travels vertically inside the filtering mass and is collected on the lower side by a system of draining pipes. The vertical flow plate filter is not a part of the proposed design (see fig. 5) and does not meet the zero energy treatment principle, due to the fact that it needs a pump to distribute the influent flows on the surface of the filtering mass. Disinfection is performed by the shallow aerobic biological pond, with a depth between 0.5 and 1.0 m [17]; in the case of aerobic ponds the oxygen diffusion is carried out through the water surface. For organic loadings lower than 4 g (CBO)/m2 day, the oxygen diffusion on the water surface is enough to meet the requirements of the treatment process. The oxygen intake on the water surface increases with low temperatures and turbulences caused by rainfall, wind, etc. 3.2 Zero energy treatment plant sizing The design stage of the zero energy treatment plant requires knowledge regarding a series of technical regulations, identified by specific flows, building and functional values, conditionings regarding adaptation to the land, etc. The mechanical stage represented by the multifunctional anaerobic filtering biological reactor is sized on the basis of the data presented synthetically in table 7.

Table 7. Design data summarizing table for the multifunctional anaerobic filtering biological reactor

Material

Parameters

Versions *concrete prefabricates, plastics

(PCV, PP, PE) or round or rectangular cross section GRP.

*built on site

Hydraulic retention time (HRT)

2 - 4 h for the first compartment 16 - 24 h for the second

compartment 24 - 48 h for the third

compartment Hydraulic loading rate

(HRL) 0.55 – 0.8 m3/m3 day

Organic loading (HRQ) 65 – 150 g(CBO)/m3 day

Treatment efficiency 50 - 60% (MTS)

70% -90 % (CBO5) 65% - 85% (CCO)

Crust evacuation interval 1 – 3 years

Sludge evacuation interval 1 – 3 years

Accumulated sludge quantity q s sludge=0.005l/g (CBO5)

Specific waste water flow 100 - 150 l/c/day

Volume VT = VTuseful + Vcrust + Vsig (m3) Crust height 0.30 – 0.40 (m) Safety height 0.1 (m)

Height 1.2 –2.5(m) Rate of climb 1.0 – 1.8 (m/h)

The secondary and tertiary steps are sized with the P-k-C* [7] method, expressed with a relation of

(1)

where: Ci is the pollutant concentration of the influent flow, in mg/l; Co is the pollutant concentration of the influent flow, in mg/l; C* - the background pollutant concentration, in mg/l; K - treatment (elimination) efficiency coefficient, in m/year; P - dynamic coefficient represented by the number of compartments in the series; q - hydraulic loading, in m/year. The great advantage of this method is that it allows for the determining the results of operating the plate filter in various hydraulic conditions and for various temperatures.

Conceptually, this is a serial compartment model; the (P) parameter expresses both hydraulic effects and pollutant elimination efficiency effects. Compared to classic sizing methods identified by using empirical coefficients and first order equations [16], the P-k-C* method has the advantage of allowing to determine the area needed individually for each pollutant, so that the final area is adopted as the largest area, needed to eliminate the least degradable pollutant, usually nitrogen or phosphorus. The zero energy treatment plant (see fig. 3) was implemented for sewage treatment for a 250-inhabitant settlement, using a lower flow horizontal plate filter (see fig. 6). The data taken into account for the design are presented synthetically in table 8;


ISBN: 978-960-474-370-4 124

these are the data according to technical regulations (table 2); the sizing results are presented in table 9.

Table 8 Zero energy treatment plant design data

No. Name Value 1 Number of inhabitants 250LE 2 Specific sewage flow 150l/c/day 3 CBOinfluent/effluent concentration 300/25 mg/l 4 Ninfluent/effluent concentration 30/2 mg/l 5 Pinfluent/effluent concentration 5/1 mg/l 6 Temperature 15oC

Table 9 Zero energy treatment plant building

features

Primary step Secondary step Tertiary step

V CBO N P CBO N P m3 m2 m2 m3 m2 m2 m3

27.47 156 1229 949 77 218 193 It is thus observed that in order to treat the sewage for the 250 inhabitants, a treatment plant consisting of multifunctional anaerobic filtering biological reactors with a total volume of 27.47m3, representing the primary step. For the secondary step 156m2 are needed to eliminate (CBO5), 1229 m2 to eliminate nitrogen and 949 m2 to eliminate phosphorus, choosing the area with the highest value, 1.229 m2 needed to eliminate nitrogen. In the case of the tertiary step 77 m2 are needed to eliminate (CBO5), de 218 m2 to eliminate nitrogen and 193 m2 to eliminate phosphorus, choosing the 218m2 are needed to eliminate nitrogen. The values determined for treatment efficiencies are 94.66% in the case of (CBO), 93.55% in the case of (N) and 89.69% in the case of (P), thus meeting the requirements to eliminate the influent flow into the emissary.

Fig.6 Lower flow horizontal plate filter - overall view

Knowing that on site values of influent flows and pollutant loads are much under the normal values, the sizing of the zero energy treatment plant was simulated taking into account the parameters (see table 10) representing the pollutant values determined on site in the case of the 950 inhabitant settlement (see table 4); the return flow value representing the average value of the case studies [11] and the sizing results are presented synthetically in table 11.

Table 10 Zero energy treatment plant design data

No. Name Value 1 Number of inhabitants 250LE 2 Specific sewage flow 50l/c/day

3 CBOinfluent/effluent concentration 84.54/25 mg/l

4 Ninfluent/effluent concentration 28.82/2 mg/l 5 Pinfluent/effluent concentration 3.32/1 mg/l 6 Temperature 15oC

Table 11 Zero energy treatment plant building

features

Primary step Secondary step Tertiary step

V CBO N P CBO N P m3 m2 m2 m3 m2 m2 m3

5.45 84 1055 689 39 189 163 It is observed that for the same treatment efficiency values the determined construction sizes are smaller compared to the case implemented according to the values regulated by the technical regulations: 80% lower in the case of the primary step, 47% lower in the case of eliminating only the biochemical oxygen consumption related to the secondary step and 49.35% lower in the case of eliminating the biochemical oxygen consumption related to the tertiary step. Nevertheless, the adopted sizes of the secondary and tertiary steps are only 15% smaller, due to the very close value of the nitrogen content of the influent flow, 28.82 mg/l in the case of the simulation calculation, compared to 30 mg/l. The comparative study highlights the importance of on-site determination of the influent flows parameter values used for zero energy natural process treatment plants. 4 Conclusions Today, sustainable development is imposed as a necessity, in the context in which climate change, excessive energy consumption, spilling large amounts of waste in the environment, poverty and


ISBN: 978-960-474-370-4 125

social exclusion, faulty management of natural resources, the extinction of biodiversity, and the improper use of soils are common situations, affecting the planet's population on the long term. In this context, the implementation of zero energy sewage collection and treatment systems is undoubtedly a truly sustainable solution, respecting the basic principles regarding environmental protection, in harmony with the social and cultural integration within the settlements where they are used. The zero energy treatment plant, using natural processes represents a possible solution, an affirmation supported through on site calculations and measurements presented in the paper, being a robust highly effective, flexible and adaptable solution, with easy implementation in any conditions, as resulting from the application implemented in the case of the 250 inhabitant settlement, out of which only the horizontal flow plate filter was presented in the paper (see fig. 6) References: [1] Igor Bodik, Peter Ridderstople, “Sustenable Sanitation in Central and Estern Europe”, Global Water Partenership 2007. [2] NP 089-2003 „Normativ pentru proiectarea construcţiilor şi instalaţiilor de epurare a apelor uzate orăşeneşti”; ('Regulations for the design of municipal sewage treatment constructions and installations'). [3] Normativ privind condiţiile de evacuare a apelor uzate în reţelele de canalizare ale localităţilor NTPA 002/2005; ('Regulations regarding the evacuation conditions of waste water in municipal sewage networks'). [4] European Directive 98/15/EC/1998. [5] Greywater Management in Low and Midel Income Contries, Eawag 2006. [6] Normativ privind stabilirea limitelor de încărcare cu poluanţi a apelor uzate orăşeneşti la evacuarea în receptorii naturali” NTPA 001/2005. ('Regulations regarding establishing pollutant load limits in municipal waste water for evacuation into natural receptors'). [7] Robert H. Kadlec; Scott D. Wallace „Treatment Wetlands, Second Edition”, 2009.

[8] KM Foxon, S. Pilay, T. Lahandbandur, N. Rodda „The anaerobic baffel reactor (ABR): An apropiate tehnology for on site sanatation”, 2004. [9] Fernanda M. Ferraz, Aline T. Bruni, Vanilod L. del Bianchi,“Performance of an anaerobic baffled reactor (ABR) in tratament cassava wastewater”, 2009. [10] Heike Hoffmann, Cristoph Platzer, Martina Winker, “Subsurface flow constructed wetland for greywater and domestic wastewater treatment”, 2011. [11] Gheorghe BADEA, Dan MUREŞAN, Ioan GIURCA, Călin Ovidiu SAFIRESCU, Ioan AŞCHILEAN, “Study regarding the determination of specific flows of westwater for rural localites”, in the Book “Recent Advances in Urban Planning and Construction - Energy, Environmental and Structural Engineering Series|20”, Proceedings of the WSEAS International Conference on Urban Sustainability, Cultural Sustainability, Green Development, Green Structures an Clean Cars (USCUDAR ’13) and Proceedings of the WSEAS International Conference on High - Performance Concrete Structures and Materials (COSTMA’13); ISSN:2227-4359; ISBN:978-960-474-352-0, Budapest, Hungary, December 10-12, 2013, pp. 101-107. [12] Cristopher M. Weedon „Compact vertical flow reed beds for tertiary sewage treatmeant”, CWA Wakefield, 2011. [13] Tom Headley, Jaime Nivala, Kinfe Kassa, Linda Olsson, Scott Walace, „Comparation of eight subsurface flow wetland design for sewage treatmeant”,CWA, 2011. [14] Steen Nielsen, David Cooper „Dewatering sluge originating in water treatmeant works in reed beds systems”,CWA, 2012. [15] Andreas Ulrich, Stefan Reuter, Bernand Gutterer, „Descentralised wastewater treatment systems and sanitation in developing countries”, Borda, 2009. [16] United States Enviromental Protection Agency „Constructed wetlands treatment of municipal westwaters”, EPA, 2000. [17] E. Thilly, C. Luthi, A. Morel, C. Zurbrugg, R. Schertenlaib, „ Compendium of Sanitation Systems and Technologies”.


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