,_ :£<#•-••• STABILIZATIONPON ^ NATIONAL LABORATORY OF CIVIL ENGINEERING PREPRINTS 0 LISBON, 1987 INDEX THEME 1 - POND EXPERIENCE 1,1 THEME 2 - INDUSTRIAL WASTES AND TERTIARY TREATMENT 2.1 THEME 3 - MICROBIOLOGY AND PHYSICOCHEMISTRY 3.1 THEME 4 - POND BENTHOS 4.1 THEME 5 - POND DESIGN 5.1 THEME 6 - HIGH-RATE ALGAL PONDS • 6.1 THEME 7 - MACRDPHYTES 7.1 THEME 8 - REUSE 8.1 - POSTER PAPERS P.I THEME 1 POND EXPERIENCE WASTS STABILIZATION PONDS IN EUROPE : A 3TATS OF THE ART REVIEW M. VUILLQT, C. 3O0TIJJ CSMAGREF, Division Qualita des Saux, Peche et Pisciculture 3 Quai Chauveau S9336 LYON Cedex 09 - Franca WHO Collaborating Cent«r for Rural Sanitation ABSTRACT Waste stabilization ponds can be found in 16 countries in Europe. Information given at a consultation of WHO specialists to review the state of the art in lagooning, highlighted the varying development stages which have been achieved in this field in 10 different coun- tries. Design criteria vary from one country to another, to suit local conditions and con- form with the quality standards which effluents are expected to meet. Lagooning has found many different fields of application in Europe : small communities, tourist areas, tertiary treatment, where it is likely to be further developed. KEYWORDS Waste stabilization ponds, lagooning, wastewater treatment, Europe, review report. INTRODUCTION In many countries, waste stabilization ponds -WSP- are one of the techniques available for the treatment of wastewaters before they are discharged into the environment. However! the design and construction, as well as the fields of application of this process vary from one country to another, and even within the same country, depending on local condi- tions. A first comparison of the various lagooning techniques used in Europe was made at a specialists' consultation organized jointly by WHO Regional Office for Europe and CEMAGREF in Lyon (France) from the 20th to 23rd October 1986. 32 experts, representing the techni- cal experience of 10 European countries and 3 countries outside Europe, attended the meeting. This paper is largely based on information received during the consultation preliminaries and from working documents prepared by the invited participants. It also reviews some of the findings of the working groups. This report exclusively refers to European countries, and to non aerated ponds;mechanically aerated lagoons although they are sometimes included in WSP statistics for individual countries, are not considered, as they differ, in our opinion, as far as both their functioning and their applications are concerned. THE DEVELOPMENT OF LAGOONING IN EUROPE The use of ponds to accumulate and treat wastes with a high content of organic matters of animal and domectic origin is an ancient method. In Europe, one could 3ay that farm ponds, which are well known in certain regions, or fishponds enriched with organic wastes, which have been developed in Central Europe sines the Middle Ages, are the earliest examples of the use of the self-purification process which takes place in stagnant ponds and of their ability to transform and recycle organic matters. The oldest WSP in Europe, still 1.1 operating today, ara probably the "Fischtgiche" bull: arounc :?;3 as a tertiary wastewater treatment for the City of Miinchen <3avaria, ~SG). The plant -overs a total area of 233ha (576 acres) divided into ponds of 7ha (!7,3 acraa) . It receives part of tile affluents of the biological treatment plant or the city, ;apprcxiaataiy 50 %. i.e. 3mVs, diluted in river water) in addition to stormwater after primary settlement. Carps breed and ara regu- larly harvested in those ponds (CEMAGREF 198*5). However, this is a totally unique case. As from the 1940'3, WSP wers developed in Denmark cor ths secondary treatment of domestic or industrial wastewaters, according "o specific purification criteria (WHO, 1986a). A first WHO survey conducted in 1964 and mentioned by Gloyna (1972), showed that WSP were used in 39 countries, including 7 European countries -• Fiadland, FB.G, GDR, the Netherlands, Rumania, Sweden, USSR. Twenty two years later, in 1986, WSP are found in at least 16 European countries : the map below gives a summary of their distribution, according to the information available. Existing operational toSP. Technical documentation available -Q. Operational WSP reported. No sufficient technical documentation No operational WSP reported. No information Fig. 1 : Map showing MSP distribution in Europe 1.2 Vcre :r lass complete technical data is avaiiabi-t for '0 2-'.z vi "."^ ' •? cc-ntries where Wi? ar^ ;sed. Trier's are however a dozen countries on which 7.0 .-»;,iA.3'i.s iazzTrrsz^on is svai- lid-2 as -3 the existence or not jf operational WSP. If ;r.s rsc'^rs -j the :o countries :r3^ vr.ich information is available, it appears that WSP nav* rsacr.aa varying development from one country za another. One can distinguish betrveer, -h» f ;i_Lc**in-3 cases : - Countries where the technique is largely developed and coaimonly ^-n piemen ted by engineers, as in che case of FRG (more than 2000 operational plant3) and ?rar,c» (al.Trost '500 plants) - Countries which have begun to collect local data on WSP from operating pilot plants and which favourably consider the use of this process. These include Portugal (more than 30 operational WSP), Spain (more than 10 operational MS?) and zo a certain extent, Belgium (variable situation, depending on the regions) and Switzerland (fairly limited applica- tions ) . - Countries where MSP have been used, but where future development is unlikely, for various reasons (geographical situation, regulations,...) as in Denmark (56 WSP presently opera- ted, generally old ones progressively being replaced by conventional wastewatar treatment plants), in Hungary (unfavourable geological conditions), and the United Kingdom (were WSP seem to be considered only for the tertiary treatment of conventional wastewater treatment plant effluents). A SURVEY OF TECHNICAL PRACTICE Table 1 below gives a summary of some of the technical data on WSP in 8 European countries from which detailed information was available. Thia data is further developed in the follo- wing paragraphs. Plant design Two treatment lines are to be considered from a. design point of view, depending on whether the plant includes a primary aneorobic pond, or settlement pond as it is called in FRG. Anaerobic ponds, which are used in many countries, have so far practically never been used in Belgium, France, Hungary because of the potential odour nuisance. Aneorobic ponds are usually designed according to the retention time of affluents: 5 to 6 days in Denmark, 1 to 2 days in FRG (taking into account the sludge volume which may reach 50 % of the total volume before desludging). Experiments Conducted at FRIELAS (Portugal ) have shown a 44 % reduction in BOD,., for a theoretical retention period of 1.6 days (i.e. : VA = 0.2 mVinhab. ec.HDO NASCIMIENTO et al, 1985). In all countries, anaerobic ponds are followed by one or several facultative or maturation ponds. The total surface area of these ponds varies, depending on local design practice, from 5 to 10 mVinhab. eq. aver 1, 2 or 3 ponds. Work carried out in Bavaria (WHO 1986,c) shows that up to 10 m! (covering. 2 ponds) the increase in specific surface area coincides with an improvement in the discharge quality (BOD5, COD), whereas beyond that surface, no further improvement is detected (except for NH.-N). The Frielas experiment (A.-F -M treatment line) shows a 94 % reduction on filtered SOD., with a size corresponding to a specific surface area (F + M) of 4.5 mVinhab. eq D(according to DO NASCIMENTO et al, 1985). ',. The treatment lines without anaerobic ponds ("facultative treatment lines") can be found in all the countries refered to except Denmark. The total specific surface area of the plants variss from one country to another, from 5 to 18 mVinhab. eq.. Some plants may consist of only one pond but as a rule, there are 2 or 3 ponds in series. The primary facul- tative pond then covers between 30 % (FRG, Switzerland) and 50 % (3elgium, France) of the total surface arsa of the plant. Available data in France shows that the size generally applied (10 mVinhab. eq. , surface ratio 2/1/1) provides a treatment quality which conforms with French standards. These are : filtered BOD. < 40mg/l; TSS < 120 mg/1. The quality of the discharge is improved when the plant is under-loaded, which is. often the case (P. BOUTIN, 1987). On the other hand, it can be temporarily inferior, particularly in Summer in the Southern part of the country, due to a high concentration of algae. The Frielas experiments on a similar treatment line (8 mVinhab. eq. surface ratio 2/1/1) shows a 95 * reduction in filtered 30D,, with very little variation over time (standard deviation less than 2). 3 1.3 : ?eviaw of WS? currant practice in S aurspean countries Csumzry .'.'b =f WSP Siza Type of WSP Type of Seaiark - design (r^f .• (inhab. aq.! influent • :) (2) (3) (4) (5) • - [4] 150 F D Data rafer to Walloon (WHO, 1995b) 7700 region SF - 5 to 11 DANEMAFX 66 50 A 0,1 VA 0.3*S? - 8 to 10 (WHO,1996a) [500-1000] 3000 FRG 2000 100 F northern Germany (WHO,1986O SF * 10 to 15 to (3 ponds-surf ratio= 3/4/3) 1000 and + A Southern Germany VA=0.5+SF« 5 to 10 FRANCE 1500 • 100 F (95%) SF-10 (2 or 3 ponds (P. BOUTIN [600] surf ratio 1/1 or at al,1987) 2/1/1) 6000 TT (5%) few I SF = 5 PORTUGAL 30 300 A I various design j (SANTOS (20 for [4300] See reports on axpe-I OLIVEIRA et) domestic ww) 15000 A (3 plants) rimentations