ECOSAN: Ekolojik evsel atıksu yönetimi

Özet

Son yıllarda gündeme gelen ve ekolojik evsel atıksu yönetimini benimseyen ECOSAN (Ecological Sanitation) yaklaşımına göre evsel atıksu bir kirletici değil yeniden değerlendirilerek kullanılabilecek bir kaynaktır. Bu yaklaşımda ayrıca, kaynakta kontrol ve nütrient döngülerinin tamamlanması gibi konular ön plana çıkmaktadır. Buna göre, evsel atıksuların kaynağında fraksiyonlara ayrılarak toplanması ve her bir fraksiyonun özelliklerine uygun olan bir dizi işlemden geçirilerek tekrar kullanımda değerlendirilmesi önerilmektedir. Bu çerçevede, sarı su (yellow water), kahverengi su (brown water) ve gri su (grey water) şeklinde fraksiyonlar tanımlanmaktadır. Tuvalet haricindeki sulardan oluşan ve en çok organik madde yönünden zengin olan gri su, bu fraksiyonlardan en az kirletici özelliğe sahiptir ve bu akımın gerekli arıtımdan sonra sulama ve yeraltı suyu beslemesi gibi yollarla su döngüsüne geri verilmesi önerilmektedir. Kaynakta ayrılarak toplanmış insan idrarından oluşan ve evsel atıksuların içindeki azotun % 90’a yakın bir kısmı ile fosfor ve potasyumun da yaklaşık yarısını içeren sarı suyun tarımda gübre olarak kullanımı, organik madde, potasyum ve patojenik mikroorganizma yönünden zengin olan ve esasen ayrı toplanmış insan dışkısından oluşan kahverengi sudan ise bir dizi işlemden sonra biyogaz üretiminde ya da toprak şartlandırıcısı olarak yararlanılması öngörülmektedir. Kavramsal çalışmaların Almanya ve İsveç’te, uygulamaların ise Asya ve Afrika ülkelerinde daha yaygın olduğu izlenen ECOSAN’la ilgili olarak ülkemizde de çalışmalar başlatılmıştır. Bir arıtma teknolojisinden ziyade evsel atıksu yönetim yaklaşımı olan ECOSAN, hem altyapı hem de arıtma / işleme yönünden konvansiyonel yaklaşıma göre önemli farklılıklar göstermektedir. 2000’li yılların konsepti olan ECOSAN gerek araştırma gerek uygulama açısından çok açık bir alan sunmaktadır.

Abstract

The emerging sanitation and wastewater management concept of the recent years Ecological Sanitation (ECOSAN) claims that domestic wastewater is not a waste to be discarded but a source to be revaluated. Within that context, various domestic wastewater fractions are separated at their source of origin, collected, stored and processed as necessary as different streams. Basically three fractions are defined: grey water, yellow water and brown water. A very important advocation of ECOSAN is the closing of material loops, especially those for the nutrients. Grey water which is all but toilet wastewater, constitutes about three fourths of conventional domestic wastewater and is the fraction which is the weakest among the three in terms of pollution potential. As such, its final reuse in the water cycle is suggested. The use of processed grey water as irrigational water or as a source for groundwater recharge is recommended after treatment mainly to provide organic matter removal in various biological treatment systems. Yellow water consists of source separated urine at its origin. This fraction is rich in terms of nutrients and contains nearly 90 % of the nitrogen and over 50 % each of phosphorus and potassium in domestic wastewater. As such, its use in agriculture as fertilizer is recommended after storage for hygienic reasons. Storage periods of up to six months are recommended for the complete destruction of pathogens. During storage characteristics of urine change significantly, especially in terms of the form of nitrogen, as urea is converted into ammonium, and in terms of salinity. Work undertaken in the field of processing and reuse of yellow water has mainly concentrated on the direct application of urine onto agricultural fields. The results from such efforts have given results comparable to synthetic fertilizers from the point of view of crop production; however the need for further research regarding the possible fate of pharmaceuticals and hormones from urine together with the issue on salinity has also been brought to attention. A group of work, although more limited in number, has also been presented in the literature directed towards the indirect use of urine for agricultural purposes, for example upon processing with the natural zeolite clinoptilolite or struvite precipitation. Brown water on the other hand is mainly separately collected human feces at its origin. This stream contains the majority of pathogenic microorganisms, nearly half of each of organic matter and potassium in domestic wastewater. The use of brown water for biogas production upon anaerobic digestion or as soil conditioner after composting is suggested. Clearly, the practice of ECOSAN at the large scale as a new means of domestic wastewater management necessitates the installation and construction of relevant infrastructure which will be considerably different form their conventional counterparts, like toilets which can separate yellow and brown water fractions, and processing units together with storage facilities. Guidelines and limits regarding the reuse of domestic wastewater fractions are extremely limited at this time, and the existing ones given by the World Health Organization are directed towards the deactivation of pathogenic microorganisms and the routes of application of the urine onto agricultural fields. Setting of limits and guidelines in terms of concentrations of constituents is a very significant issue which is yet to be handled. The majority of the work devoted to the subject matter in terms of conceptual research seems to be generated mostly in Germany and Sweden, while the majority of practical applications are conducted mostly in Asian and African countries. Although limited in number, ECOSAN related research is also on the way in Turkey as well, and most of those efforts are directed towards alternatives devoted to the indirect use of urine in agriculture together with alternatives related to the treatment of grey water. ECOSAN seems to be one of the developing concepts of the future and ECOSAN related research is one of the open areas in environmental engineering, as well as in terms of practice and practical applications.