Wastewater System Design

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Wastewater systems are as simple as a septic system for a single-family house or an isolated commercial property, or much more complex.  Large wastewater treatment systems consist of the collection system (gravity sewer lines, manholes, and sometimes lift stations and force-main sewer lines), the actual wastewater treatment plant, and the discharge point, land application area, or other treated-water disposal method in use.

On-site sewage facility (OSSF) systems may include:

• standard (“conventional”) septic systems for single-family homes;
• aerobic septic systems are used when soil or ground-water conditions won’t allow the conventional approach;
• clustered systems (could be standard, aerobic, or other more unusual approaches) for multiple residences, small commercial centers, etc. – these may require special covenants, conditions and restrictions (CCR’s) tied to the deed(s), as well as County or State review and permitting, depending on size of system.

Centralized, “package” plants or larger and more regional wastewater plants may be of designs such as:

• trickling filter treatment, with microbial colonies grown on special, high-surface-area packings in beds or towers, with air bubbled through the packing material for oxygen supply in aerobic treatment processes;
• extended aeration treatment, using activated sludge (live aerobic microbe culture) mixed into the raw wastewater and aggressively agitated/aerated;
• membrane bio-reactor (MBR) technology, involving the growth of microbial colonies on special membranes, with the wastewater forced through the membranes and past the “bug” colonies using pressure.

In any of these “bigger plant” wastewater treatment setups, aerobic microbes are used to break down a great percentage of the organic waste.  Anaerobic microbes are used to break down ammonia and other nitrogen wastes present in the sewage, or generated by the aerobic operations.  Other “tertiary” treatment methods may also be used to reduce the amount of “biochemical oxygen demand” (BOD), “total suspended solids” (TSS), and other contamination types before the wastewater has been treated sufficiently, and is deemed clean enough for release.

This treated water may be disposed of in a number of ways.  First, if it is treated sufficiently, it may be released to a surface water body, such as a dry stream bed, a creek, a river, a lake or the ocean.  Sometimes the treated water will be “land-applied,” sprayed or dripped into the shallow ground, in specially prepared and protected land areas.  Or the water may be “reclaimed” and used for beneficial purposes, such as being piped into plumbing systems for flushing toilets, landscape irrigation, and other practical applications.  When water from the wastewater plant is treated to “almost potable” standards and put to these uses, less potable water has to be provided to the remainder of the project, and ongoing operations.  This is a great approach in geographies with limited water resources.

Wastewater plants may also be built with no noise or odor nuisance. Variances from TCEQ can reduce the buffer zone requirements for plants that are fully enclosed. (See examples at Aqueonics)

Chapman Engineering also specializes in Lift Station System Design (Like the one pictured above).  Lift stations are commonly used in parts of a wastewater collection system, for those properties that lie below the elevation that can be served by gravity sewer mains.  We work in conjunction with quality vendors and installation contractors to provide years of trouble-free service.  If you have a project with topography that prevents use of a gravity sewer system, allow us the opportunity to design a lift station that will suit the needs of your project.  Chapman Engineering also provides cost estimates and tries to help describe the economics of this approach, in the context of each development.

Residences, subdivisions or new additions to municipal systems need engineered wastewater system designs. Depending on system size, there are municipal, county and TCEQ standards and permits which apply to the project.