Sewage treatment plants (wastewater treatment, effluents, disposal). Intensive reactors and extensive reactors: waste stabilization ponds, wastewater reservoirs, activated sludge, trickling filters, UASB, aerated lagoons, SAT constructed wetlands. Sanitation. Consulting, consultants, conceptual engineering, process design

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Sewage treatment technologies
(wastewater treatment)

The wide spectrum of available technologies for the design of sewage treatment plants.

The design of sewage treatment plants (also called "wastewater treatment plants") includes several treatment units, typically:

Pre-treatment: one or more units for the physical separation of gross solids (sand, litter) and flotables (FAT, oil and grease, etc.).
Biological treatment: one or more types of biological reactors in series.
Clarification, disinfection and post-treatment of treated wastewater (when required).
Sludge treatment (some sewage treatment plants do not require sludge treatment).

There exist numerous types of biological reactors for sewage treatment.

They can be classified according to:

Process biochemistry:

Aerobic process (e.g., activated sludge, wastewater maturation ponds, trickling filters, high-rate stabilization ponds).
Anaerobic process (e.g., anaerobic ponds, UASB-Upflow Anaerobic Sludge Blanket reactors).
Facultative process (or mixed) (e.g., facultative ponds, some constructed wetlands, wastewater reservoirs).

Process intensity:

Intensive reactors (e.g., activated sludge, UASB anaerobic reactors, high-rate trickling filters).
Super-Intensive reactors (e.g., membrane reactors, activated sludge combined with fixed biomass).
Extensive reactors (e.g., waste stabilization ponds, wastewater reservoirs, SAT-Soil Aquifer Treatment, constructed wetlands, macrophyte ponds).
Semi-intensive reactors (e.g., anaerobic ponds, low-energy aerated lagoons, low-rate trickling filters, high-rate stabilization ponds).

Operational regime:

Continuous flow reactors (e.g., continuous flow activated sludge, UASB type anaerobic reactors, trickling filters, stabilization ponds, constructed wetlands, macrophyte ponds).
Sequential batch reactors - SBR (e.g., sequential batch activated sludge, sequential batch wastewater reservoirs).
Pulse reactors (e.g., some types of vertical flow constructed wetlands, intermittent sand filters).
Perfectly mixed and plug-flow reactors.

Biomass characteristics:

Suspended biomass reactors (e.g., activated sludge, UASB type anaerobic reactors, stabilization ponds, aerated lagoons).
Fixed biomass reactors (or biofilm) (e.g., tickling filters, SAT, constructed wetlands, macrophyte ponds, rock filters, intermittent sand filters).
Combined biomass reactors.

Selecting the best technology for wastewater treatment in a specific project.

No one of the above technologies is definitely better than the others.
Each one has its advantages and disadvantages regarding construction costs, operational costs, energy use, size, operation simplicity, stability, reliability, etc.
Each one suits better to different specific conditions.

One of the most difficult tasks in the conceptual design of a sewage treatment plant is the selection of the most appropriate technology for the specific conditions of the project.

The designer should obtain an optimal combination of:

High public health and environment protection.
Low construction and operational costs.

A proper conceptual design is a key element for the technical success of the project: good quality effluents, simple and reliable operation, low costs, low environmental impact.

The present trend in Israel and many other countries is to move from the design of sewage treatment plants as an isolated event, towards design within the framework of regional environmental planning.

The geographic unit defining a region is generally the catchment basin (watershed in American English). Thus, catchment basin planning based on wide public health and environmental considerations is substituting the relatively simple sewage treatment plant design as an engineering practice.

The conceptual design of sewage treatment plants within the catchment basin framework goes beyond the classical engineering profession, and requires the involvement of a multidisciplinary team of professionals.

There are many new technologies, many of them patented under novel names (PPRT, RPt, MMBBRR, "dynamic bed", etc.) and all of them claiming to be the best.
An independent consultant knows ALL of them but sells NOONE of them.
Thus, an independent consultant can objectively compare them and tell you which is the best for your problem.