wastewater46

Wastewater Treatment Technology

Introduction
The five main wastewater treatment technologies covered in these Sanitation Connection pages are:

waste stabilization ponds (WSP),
wastewater storage and treatment reservoirs (WSTR),
constructed wetlands (CW)
chemically enhanced primary treatment (CEPT), and
upflow anaerobic sludge blanket reactors (UASBs)

An introduction to WSP and WSTR are given in the two pond design manuals by Mara (1) and Mara & Pearson (2) in the attached list of publications (under Stabilization ponds). These list pond advantages and perceived disadvantages, and describe how ponds work and how they should be designed, operated and maintained, and monitored and evaluated.

Constructed wetlands, often referred to as reedbeds (as reeds are the plant most commonly used) are described in the design guidelines by Merz (3) in the attached list of publications (under Constructed Wetlands).

CEPT is the coagulation/flocculation of raw wastewaters with lime or aluminium sulphate or ferric chloride or sulphate (often with polyelectrolytes) followed by primary sedimentation (ie, as commonly used in water treatment but with much higher chemical doses). It is described in the introductory note by Chagnon (4) in the attached list of publications (under Chemically Enhanced Primary Treatment).

UASBs are really highly efficient upflow septic (or, more correctly, Imhoff) tanks. They have hydraulic retention times of 8-12 hours when treating domestic wastewaters in warm climates (rather than 1-2 days as in anaerobic ponds, although the high-rate anaerobic ponds developed by Peña Varón (5) have retention times of only ~12 hours). UASBs are best described in the book by van Haandel and Lettinga, Anaerobic Sewage Treatment: A Practical Guide for Regions with a Hot Climate (Wiley, 1994) (which unfortunately is not available in electronic format). An excellent on-line introduction to UASBs is given by Field and Sierra (6) in the attached list of websites (under UASBs).

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