Management and treatment of wastewater and drainage system design using BIM-MEP software
The treatment and reuse of wastewater are indispensable challenges in the perspective of environmental sustainability and the optimization of natural resource use. Managing the entire water cycle certainly allows us to return a precious resource to use that otherwise would be wasted.
The water cycle begins with the collection of wastewater. Let’s start right there and see what wastewater is, how it is treated and what tools to use for properly designing and sizing a drainage system.
What is Wastewater
In the field of environmental and chemical engineering, wastewater is all water that, after use, requires purification treatment before being reintroduced into the natural environment or reused.
Depending on their origin, they are:
- domestic wastewater, from residential areas and services, mainly from human metabolism and domestic activities (such as hotels, schools, barracks, public and private offices, sports and recreational facilities, retail and wholesale stores or bars). They mainly contain cellulose, lipids, proteins, urea, uric acid and carbohydrates;
- industrial wastewater, any type of water from buildings where commercial or manufacturing activities take place. The characteristics of such effluents vary depending on the type of industrial activity and are classified as hazardous or non-hazardous to the environment;
- urban wastewater, a mixture of domestic, industrial, and/or runoff water (rainwater runoff, road washing water, etc.) conveyed in sewer networks from an urban area and destined for treatment at an urban wastewater treatment plant.
These waters are further characterized based on various physical, chemical and biological parameters present in wastewater.
The parameters used to characterize wastewater are:
- physical parameters
- electrical conductivity
- chemical parameters
- O2 demand: chemical oxygen demand (COD), biochemical oxygen demand (BOD), total oxygen demand (TOD)
- total organic carbon (TOC)
- nitrogen: ammonia, organic, nitrites, nitrates
- phosphorus: orthophosphates, polyphosphates, organic
- oils and fats
- mineral oils
- toxic substances
- dissolved oxygen
- biological parameters
- total coliforms
- fecal coliforms
- fecal streptococci
- Escherichia coli
“Social, productive and recreational activities, especially in urban contexts, require a considerable amount of water. The use of water inevitably generates discharges that must undergo purification treatment before being returned to the environment. Urban wastewater, once primarily composed of biodegradable substances, now faces growing challenges in its disposal due to the widespread presence of synthetic chemical compounds, particularly used in industry.
Seas, rivers and lakes cannot tolerate an increase in pollutants beyond their self-purification capacity without compromising water quality and ecosystem balance. Therefore, the need to treat wastewater through systems that simulate natural biological processes occurring in water bodies is evident. Wastewater treatment is particularly intensified when receiving water bodies (seas, rivers, lakes, etc.) are at risk of permanent pollution.
Biological treatment processes rely on artificially recreated natural phenomena, allowing optimal control of parameters regulating these processes. Biological purification involves communities of living organisms, such as bacteria, algae and microfauna. Which degrade pollutants through mineralization processes and accumulation in sludge separable from water by sedimentation.
Regardless of the environmental impact, proper water cycle management involves the reuse of treated wastewater as an alternative for more rational water resource use. This approach offers social and economic benefits, such as protecting water bodies and proper water resource management. The reuse of wastewater can be considered an innovation in the sustainable use of water reserves, providing water supply at lower costs than disposal.
The treatment of wastewater is, therefore, a fundamental process to remove contaminants and pollutants before returning water to the environment or reusing it safely and is generally divided into three main phases:
- primary treatment
- settling: wastewater passes through a settling phase in large tanks to separate larger particles. During this
process, sediments form and settle at the bottom of the tanks, forming the so-called primary sludge;
- removal of suspended solids: larger suspended solids are removed through physical processes such as sedimentation;
- settling: wastewater passes through a settling phase in large tanks to separate larger particles. During this
- secondary treatment
- biological process: wastewater comes into contact with bacteria and other microorganisms that break down organic matter into more stable substances, such as carbon dioxide and water;
- aeration: oxygen is often supplied to wastewater to support the activity of aerobic bacteria that accelerate the decomposition of organic matter;
- tertiary treatment
- nutrient removal: in some situations, it is necessary to remove additional nutrients such as nitrogen and phosphorus. Which can cause environmental problems like eutrophication;
- advanced filtration: water can pass through additional filters to remove smaller particles and residual impurities;
- disinfection: to ensure microbiological safety, water can undergo disinfection processes. Such as the addition of chlorine or ultraviolet irradiation.
Treated wastewater can be reused in various applications, such as irrigation, industrial cooling or recharging aquifers.
It is important to note that the wastewater treatment process may vary based on the characteristics of the incoming wastewater, local regulations and available resources.
Furthermore, wastewater treatment plants can vary in size and complexity depending on the needs of the community or industry served.
Wastewater treatment is essential for preserving water quality, preventing environmental pollution and protecting public health.
Drainage System Design
The drainage system refers to the set of pipes, fittings and equipment necessary to receive, convey and dispose used water. It usually comes from domestic sanitary appliances (such as sinks, toilets, showers, washing machines, etc.).
Domestic wastewater can be classified as:
- graywater: wastewater from washings (soapy);
- blackwater: wastewater from human metabolism;
- white or rainwater: water from natural precipitation collected by gutters and downspouts.
White water is usually separated from domestic effluents and conveyed directly into the ground. Drainage networks must facilitate rapid drainage of wastewater towards the external disposal system, avoiding stagnant accumulations. To ensure this, it is essential to create the right slopes and select appropriate diameters for the pipes. Pipes must also resist mechanical, thermal stresses and the corrosive action of sewage. The use of pipes and devices with acoustic insulation is also recommended to prevent unwanted noise.
There are different types of wastewater drainage systems currently in use. In Europe, the common practice is to size drainage branches (connected to sanitary appliances) considering a fill level of 50%, with connection to a single drain column. This technical solution aims to reduce noise levels effectively and prevent the loss of the hydraulic seal of traps.
Within a building, a drainage system consists of the following main components:
- trap: a device installed directly on sanitary appliances with the aim of preventing the passage of foul odors by creating a hydraulic seal;
- drainage branch: a pipe, usually oriented predominantly horizontally, connecting sanitary appliances to a drain column or drain manifold;
- drain column: a predominantly vertical pipe that conveys wastewater from sanitary appliances to the drainage system;
- drain manifold: a sub-horizontal pipe, installed visibly inside the building or underground. to which drain columns or sanitary appliances on the ground floor are connected;
- vent stack: a predominantly vertical pipe connected to a drain column. It purpose is to limit pressure variations within the drain column itself.
Calculation and Sizing
“Drainage systems must ensure correct water flow and direct it towards the sewerage network. These systems must guarantee various performances, including rapid drainage, absence of residues, hydraulic and gas tightness, air replenishment pushed during drainage. Above all, the correct diameter of the pipes allowing effluent evacuation without filling the entire section.
The design of a drainage system requires knowledge of the maximum quantities of water that can be discharged by individual sanitary appliances. Regulations generally provide criteria for sizing drainage branches, drain columns and manifolds based on the flow rates to be discharged at each section of the system. The sizing of drainage branches is based on a fill level of 0.5 with connection to a single drain column.
The calculation method, valid for all gravity drainage systems for the disposal of domestic wastewater, involves sizing pipes based on the units of discharge typical of appliances multiplied by a frequency coefficient (K) related to usage (for homes, it is equal to 0.5).
The design of the drainage system includes the following phases:
- calculation of the total load (average flow in l/s) on each drainage branch, summing the flow contributions of each connection and considering simultaneity;
- determination of the total load (average flow in l/s) on each drain column, summing the flow contributions of each connection and considering simultaneity;
- calculation of the total load (average flow in l/s) conveyed to the drain manifold, progressively summing the total values of all connections, of the columns that converge into it, and considering simultaneity.
It is essential to know the average discharge flow (l/s) of the sanitary appliances in the building to correctly size the drainage system pipes.
The maximum allowable capacity for pipes (Qmax) must correspond to the minimum allowable, determined by the greater value between the calculated maximum wastewater flow (Qwwmax) or the total flow. Additionally, one must consider the flow of the appliance with the largest discharge unit (DU).
The flow of water in the system occurs by atmospheric gravity, as wastewater descends due to its weight. Therefore, all non-vertical branches must slope towards the outlet. The slope of the manifolds should be as uniform as possible and range between values of 1% and 5%, with the recommended slope of 2%, to favor self-cleaning of the pipes.
The sizing of pipes must be done carefully to avoid blockages, emissions of foul odors into inhabited spaces, high drainage noise and foam returns. An undersized section hinders drainage, while an oversized section promotes the formation of deposits and sediments, with a progressive reduction in section and the possibility of clogging. Therefore, it is crucial to adopt an appropriate diameter to ensure regular drainage and effluent flow, allowing for self-cleaning action on the internal walls of the pipes.
With BIM software for MEP systems, you can create the 3D model of the system and size the pipes based on regulatory provisions. The 3D model of the system will be extremely useful both in the design phase. It ensures you avoid clashes with the structural, architectural and other systems (heating, gas, electrical, etc.) models. As well as in the maintenance and management phase.
Imagine having a leak, needing to replace an existing pipe or having to carry out demolitions. To pinpoint the precise location of pipes and other elements that make up the system, having the 3D model of the project is a great help and allows for smooth and safe action.
These are just some of the many advantages of BIM 3D modeling for the MEP system you are designing. Read these articles to learn more:
- Integrated BIM MEP Design: Processes, Advantages, and Solutions
- Integrated Plumbing System with Architectural Design: MEP Advantages
- Who is the BIM MEP Modeler.