**5.2 Waste stabilization ponds (WSP)**

202 Studies on Water Management Issues

pollutants are rather lipophilic in character, and are consequently likely to bind with the particulate matter. For this reason mechanical treatment can present an important step in elimination of these substances, but nevertheless, the absence of any biological step may have substantial effect on the total removal of more biodegradable compounds (Vogelsang

Many treatment processes in ET (e.g. nitrification, aerobic degradation of organic matter and P trapping) are oxygen-limited. Studies have shown that the amount of oxygen transferred through the plants is very small compared to the oxygen demand utilized by the wastewater under usual loading rates. Consequently, many recent studies entirely neglect oxygen transfer by plants and include plants mostly as a microorganism carrier and biodiversity factor. The inadequate oxygen transfer of typical subsurface flow wetlands resulted in the progress of improved treatment systems, which are able to assure adequate oxygen levels for nitrification, degradation of organic matter, and prevention of P leaching. The systems include introduction of oxygen to the wetland by means of regular water level oscillations, passive air pumps or powered mechanical aeration of the reed bed (Nivala et al., 2007). Yet, the elimination of nitrogen in ET has been enhanced by the different flows, cascades, open areas, and with the application of recirculation of the treated outflow back to the inflow

Removal processes of pollutants in ET can be controlled by hydraulic load, ET design as well as with macrophytes and algae. They directly and indirectly influence the physical and chemical environment in ET and play an important role in removal processes. Macrophytes e.g. enhanced sedimentation and sorption on biofilm and therefore accelerate removal of suspended solids, settleable solids, organic N, total N, COD and BOD5. Floating macrophytes shade the water surface and reduce temperature oscillations, algal development and gas exchange with the atmosphere. Wooden plants can play an important role in phytoremediation processes and evapotranspiration. Algae with photosynthetic activity cause a higher pH (and consequently ammonia volatilisation and ortho-P precipitation), P accumulation and a higher DO concentration in water (consequently higher ortho-phosphate retention and more intensive nitrification). On the other hand, algae in the effluent cause a

lower treatment efficiency of suspended solids and BOD5 (Šajn-Slak et. al., 2005).

sustainable solutions for environmental protection and restoration.

**5.1 Vegetated drainage ditches (VDD)** 

ET for water management merges vegetated drainage ditches (VDD), waste stabilization ponds (WSP) and stormwater detention ponds (SDP), TW, buffer zones, phytoremediation with dense woodland establishment, river revitalization, and in stream and bank side river techniques. One of the main aims of ET concept is to integrate exchange, combine and use multi-functionality of different kind of "green technologies" to obtain innovative and

Drainage networks of surface and subsurface drains mainly serve to remove and accumulate excess water associated with irrigation and storm events. In agricultural areas

(Griessler Bulc & Šajn-Slak, 2009; Griessler Bulc et al., 2011).

**4.4 Role of plants and algae** 

**5. ET types** 

et al., 2006).

WSP are simple man-made basins for primary, secondary and tertiary treatment of variety of wastewaters. They are used worldwide, alone or in combination with other treatment processes. Anaerobic, facultative and maturation ponds are constructed in one or several series. Anaerobic ponds are designed for primary treatment. They remove suspended solids and some of the soluble element of organic matter (BOD). Most of the remaining BOD is removed in facultative pond (secondary stage) by algae and heterotrophic bacteria. Tertiary treatment takes place in maturation pond where pathogens and nutrients (especially nitrogen) are removed. WSP are low cost treatment technology with simple operation and maintenance (Ramadan & Ponce, n.d.).
