Selection of inappropriate treatment technologies
It is important to select an appropriate treatment technology based on the type of wastewater i.e., it is effective to select a biological treatment techniques when there is high degradable and low non-biodegradable organic content present in the wastewater. If you just go with the technology which is widely used they normally fail in maintaining the microbial consortium i.e., cell count and cell viability. When the microbial consortium is not maintained, the treatment efficiency is affected. If the biological treatment facility is not effective and if you just pass through the partially treated wastewater through the filters, the treated wastewater fails in meeting the standards.
Collecting inaccurate waste stream data
It’s very important for wastewater treatment specialists to collect as much information about your waste stream as possible at the very beginning of the engineering process. Knowing the right flow rates at the initial stage of design helps to handle the treatment plant during peak flows. If you design the plant without knowing the actual peak flow, then the plant will be incapable to treat the wastewater when the flow is full and results in overflow and no treatment will happen. For example, flow rates in food processing facilities, among others, go up and down from day to day and change over time. Often, we see these facilities spend two or three days keeping track of their wastewater data. This ensures the system designers and engineers not only know the average rates but are certain of the maximums and minimums over time.
It is also evident to have the data of characteristics of the influent wastewater like the average concentration of BOD, COD, pH, etc., it is the essential information that will be factored into your system’s design. If these parameters are not considered during the design, you will likely see an increase in operational problems with your plant due to inefficiency in handling the high concentration. For example, if you design the plant to handle the BOD of 500 mg/L and the actual BOD of the wastewater is 3000 mg/L, then the plant will be incapable to handle the high BOD, hence treated water fails to meet the standards.
Improper aeration by using common air blowers for both equalization & aeration
When designing an effective biological water treatment system, it’s important to not over or under aerate the wastewater. When the system is under aerated, it runs out of oxygen, and the first thing you’re going to notice is foul odors. We notice in many of the conventional treatment plants, the system designers suggest the common blowers for both equalization and aeration. This is absolutely wrong. Because in the equalization tank, the water level will vary with time, when the water level is low, air will escape to the free head in the equalization tank resulting inadequate air supply to the aeration tank. This will affect the treatment facility. Suppose if you over aerate the system, it won’t create any operational issues, but you’ll be running aeration equipment unnecessarily, which will consume more electricity than you need and inflate costs.
Aeration tank size designed is inadequate to hold full capacity
In most of the conventional STP design, the size of the tank designed is inadequate to hold the full capacity, which does not allow the wastewater to be in contact with the micro-organisms for sufficient duration for the breakdown of complex organic matter to simpler. Also, sometimes the partially treated water or untreated water will be released or pumped urgently with the fear of overflow during the inflow with full capacity. Washout of biomass from the aeration tank has been a handicap in such technologies.
Co-Author: Arun Karunakaran