Introduction

Residents of the generic city deserve a clean and enabling environment free from effluent waste pollution of any form either to the environment or on any water sources. Water is a basic commodity that is used in nearly all domestic operations be it cooking, drinking, cleating and many other domestic applications hence the residents of Generic city at all times needs to have properly treated and clean water for domestic use and to help solve the challenge that has been in the region for decades of lack of clean and safe drinking water.

Conan & Lupin Consultant is committed to providing the residents of Generic City with efficient and effective Waste Water Treatment Plant in the town that will ensure that residents’ thirst for a clean and sustainable environment and clean and safe water for drinking and other domestic operations.  Our team has been in operation for about one month now working on the treatment plant designs and layout plan for the project that is projected to serve for over 25 years. We are committed to providing a standard design and therefore the designed plant was subjected to review by team leader as observations made are as follows.

After having several hours of scrutiny, assessment and analysis of the proposed wastewater treatment flow pipe design and diagrams.  A number of issues have been noted that need little adjustment and ratification in order to achieve the ultimate mission of the company.

Plant expansion

According to the latest trend in urbanization and industrialization and population in the past decade, the possibility of the current number of people living in Generic city shall triple is quite eminent therefore there is need to restructure the population increase projection stipulated in the design parameters by population incremental factor of 3.0 for the first 10 years and then for the last 5 years, the population increase factor of 3.5 should be used instead of the constant factor used to generate the outlined projections on the proposed design. Therefore the treatment plant needs to have enough space for expansion for the future. As per the design specifications outlined in the tender allocation documents, the plant is expected to have sufficient space for the substantive degree of pollution removal in terms of nutrients and organic matter to comply with the set legislative limits on effluent or wastewater discharge while being cognizant of construction and operating cost.

More attention is needed on the conceptual level of plant design for verification of the treatment plant’s overall performance efficiency. There is a need to elaborate more on the conceptual design stages, explaining in detail the sequence of anoxic and aerobic sections, processes of chemical additions into the treatment system and extra-treatment cycles. All these need to be explicitly

Piping material

One of the objectives is to design a system that will last for long with minimal maintenance operations. And on this account, there is a need to revise the material suggested for the design for the treatment piping systems of the plant. It is highly recommended to incorporate the use of stainless steel and carbon steel in the piping designs of the treatment plant. Traditionally, these are the metals that have been used in developing waste treatment plants due to their perceived strength.  The system is associated with scaling, corrosion, pitting and gradual pressure loss that occasionally results in frequent repair hence escalating the maintenance cost. However, we aim to maintain the maintenance and operating cost as minimum as possible.  But stainless steel has become more expensive to obtain, thus using steel in this project would make the project more costly. I, therefore, recommend the use of chlorinated polyvinyl chloride (CPVC) for piping and fittings for the piping systems in this project. CPVC is highly recommended not only because they have high resistance to chemicals and microbes used in the treatment but they also have lower installation cost plus durability and pressure rating that does not diminish over time.

Especially in the secondary treatment process where a high concentration of microorganisms is involved in washing out excessive biological growths in clarifiers, these microbes include acids such as hydrogen sulphide and dechlorinating chemicals that corrode the metal pipes. Therefore CPVC is ideal for fitting pipes in the secondary treatment systems to overcome corrosion that might be induced by these corrosive chemicals.

Parshall flume sizing deficiencies

The design of Parshall fumes for the proposed wastewater treatment plant is worth commendable. They are strategically positioned to measure both affluent and influent wastewater flows. Parshall flumes are one of the best devices used in versatile flow management due to its nature of corrosion resistance thus giving clear readings and accurate measurements. in wastewater treatment, the most challenging task is the measurement of the headworks or influents. Wastewater headworks often contain a high amount of hydrogen sulphide and grit, which often wreak havoc on the flow management devices and tools. Another notable advantage of using Parshall flumes is that it can be used to measure various interplant flows since it has a high resistance to damage therefore can be used to measure both treated and untreated effluents. Durability is a key consideration in designing long term service treatment plants as it helps in reducing repair and maintenance costs.

Diurnal variation in sewage loading

Since the plant is designed to facilitate sewerage and effluent treatment for about twenty-five years, by all standards and factors it needs to have a properly functioning effluent fluctuation control. This is so essential with regards to biological denitrification and nitrogen removal during the treatment process. From the proposed design, the prediction of diurnal variation of Generic city sewer treatment plant range from 0.68 as a minimum to 2.76 as a maximum for 24 hours each day for twenty plus years. Fine the estimation is good as it covers and considers the most active hours of the day having allocated considerable and reasonable diurnal variation, however, the challenge with the projected range is that there is no allowance on the surges that might arise in the silo tanks as results of runoff and other factors. As it stands now, if such a scenario occurs, the whole plant would stop functioning thus cutting the short supply of clean treated water to the residence of Generic city. Therefore it is highly recommended that the design and estimations of the diurnal variation incorporate room for upsurges and safety factors of allowance to accommodate the undesirable events in case they occur.  With the population projection between 2040 to 2045 shall be characterized by immense variation therefore to guarantee effective and efficient treatment this year, properly designed diurnal fluctuation needs to be installed. If this change is considered then the overall efficiency will be greatly improved since reducing COD and BOD shall be at optimum thus enhancing the variation in the quality of effluent during the day due to buffer effect of the oxygen-nitrogen conversion.

Screening channels and grit removal

The screening channels should be redesigned for the approach velocities between 3pfs (0.9 m/s) and 4.4 fps. As screening channels stand as at now, if effluent velocities drop below 3fps, there are high chances that the grit and screening might accumulate upstream of the screen. The accumulation of debris within the plant is dangerous to the plant operation and significantly reduces the overall efficiency of the plant. Presence of debris in the plant often leads to functional challenges once a peak flow flushes the debris to the screens instantaneously

Conclusion

Generally, the proposed design of the Generic wastewater treatment plant is commendable as most of the design specifications and expectations are overwhelmingly attained through design features and design parameters presented. The people of Generic city deserves a long-lasting and sustainable waste treatment scheme that will serve for more than twenty-five years, and in reference to their needs and demands, we ahn=ve to ensure that the design is perfectly polished to meet these demands. After going through the design have made necessary recommendations on the areas that need adjustments and redesign so as to help the company continues to provide a quality design to its clients.