Plantwide modelling – anaerobic digestion of waste sludge from parent nutrient (N and P) removal systems

Wastewater treatment plant (WWTP) mathematical models are based on the behavioural patterns of microorganisms involved in the treatment process. These microorganisms are assumed incapable of thinking or planning but simply act according to the capabilities afforded to them by their surrounding conditions – hence different microorganisms pre-dominate different WWTP zones according to how well the conditions suit them. When waste activated sludge (WAS) from biological nutrient removal (BNR) activated sludge (AS) systems, containing phosphorus-accumulating organisms (PAOs), is fed to an anaerobic digester, there is a release of high quantities of metals, phosphorus (P) and nitrogen (N). The manner in which we model the release of these metals and nutrients significantly affects the accuracy of predicted anaerobic digestion (AD) outcomes. Previous studies of PAOs show that in the anaerobic zone of the AS system, they can form energy-rich poly3-hydroxybutyrate (PHB) at the expense of their aerobically generated polyphosphate (PP). Thus, it is expected that the PAOs containing PP sent into an anaerobic digester with volatile fatty acids (VFAs) present, would utilize their PP reserves as they would in the anaerobic zone of an AS process ending up with formation and storage of some PHB. Ultimately, all the stored products of the PAO get released, since there is no alternating aerobic environment to cater for their growth. Since it has been established that the PP release in the AD occurs much faster than the PAO biomass hydrolysis rate, it is modelled as a separate process. Steps are presented in the development of this PP release mass-balanced stoichiometries that occur with AD of PAOs. By comparing outcomes from these proposed stoichiometries against measured experimental data, it is noticed that better predictions are obtained with acetate uptake for PHB formation than when modelling the AD PP release to occur with PAO death and hydrolysis.

Thermal and Oxygen Conditions of Lake Charzykowskie in the Years 2014-2016

This paper presents an analysis of thermal and oxygen conditions of the Charzykowskie Lake in the years 2014-2016 in the period from May to August. The measurements were carried out once a month, at points representing three different basins in the lake, and the temperatures and oxygen content dissolved in the water were recorded every 1m from the surface to the bottom at the deepest point of each basin. The changes in temperatures and content of dissolved oxygen were analysed in each of the representative measurement points for particular parts of the lake. It has been shown that the deficit of oxygen dissolved in the bottom layers of the water starts occurring by the beginning of the summer stagnation period, whereas at its peak (August) the anaerobic zone includes hypolimnion and part of the metalimnion. The hypothesis that the thickness of the thermal layers varies within the lake basin was confirmed. It was also shown that the oxygen content curve at representative points, in all years of research, evolves to the form of a clinograde at the peak of summer stagnation, where the concentration of dissolved oxygen decreases with the depth.

Modeling and Simulation of Pollutants Removal in the Modified Oxidation Ditch

The kinetic models of COD removal and phosphorus release in anaerobic zone, and phosphorus uptake, nitrification, denitrification and COD removal in circulating corridors were established in this work, in order to provide the guidance on design and running of the modified oxidation ditch. At the same time, the coefficients of reaction rates were calculated. Using the kinetic models already been established and the coefficients already been calculated to simulate the experimental results, the results showed that the models can well simulate the removal effect of pollutants in the modified oxidation ditch.

Study on the Influence of C/N Ratio on Denitrification Efficiency in CRI System

The TN removal efficiency is very low and the TN concentration of effluent can not meet the national standard of GB18918-2002 in the CRI system. In order to increasingly improve the denitrification efficiency of the CRI system, the artificial soil column is used to simulate the CRI system with 4 kinds of wastewater step-feeding modes. A series of comparative experiments are carried out, and the experimental results show that the TN removal efficiency of the CRI system is controlled by the denitrification process, and the denitrification process takes place mainly in the 900-1400mm zone of the artificial soil column; with the step-feeding mode, the C/N ratios of effluent from the 900-1400mm zone increase obviously in the CRI system, and in the case 4, the C/N ratios of effluent from the 900-1400mm zone are about 2, which is the closest to the optimal C/N ratio of the denitrification process; the best wastewater feeding mode of the CRI system is that the wastewater is pumped into the system from the infiltration media surface and the starting point of the anaerobic zone at the same time, with the influent amount ratio of 2:1.

Saving phosphorus removal at the Henderson NV plant

While the mechanism of biological phosphorus removal (BPR) and the need for volatile fatty acids (VFA) have been well researched and documented to the point where it is now possible to design a plant with a very reliable phosphorus removal process using formal flow sheets, BPR is still observed in a number of plants that have no designated anaerobic zone, which was considered essential for phosphorus removal. Some examples are given in this paper. A theory is proposed and then applied to solve problems with a shortage of VFA in the influent of the Henderson NV plant. Mixed liquor was fermented in the anaerobic zone, which resulted in phosphorus removal to very low levels. This paper will discuss some of the background, and some case histories and applications, and present a simple postulation as to the mechanism and efforts at modelling the results.

Experimental Study on the Optimal Thickness of Infiltration Media of the CRI System

In order to investigate the optimal thickness of infiltration media in the Constructed Rapid Infiltration System, the artificial soil column is used to simulate the Constructed Rapid Infiltration System, and the CODCr, NH3-N and TN concentrations of the effluent from all the sampling sites are monitored. The experimental results and analysis show that the thickness of infiltration media exerts a significant influence on the CODCr, NH3-N and TN concentration and removal efficiency of the effluent; the CODCr, NH3-N and TN are mainly removed in the 0-1800mm zone of the artificial soil column; the total CODCr removal efficiency increases, as the thickness of infiltration media increases, but the CODCr removal efficiency in the 1800-2200mm zone is very low; the NH3-N and TN removal efficiency reaches the maximum where the thickness of infiltration media is 1800mm; the NH3-N and TN concentration of the effluent from 1800-2200mm zone dose not decrease, but increase 5-8%, due to the assimilation denitrification and amemoniation reaction on the end of the anaerobic zone; in consideration of the effluent quality, efficient biodegradation zone, construction investment, etc. the optimal thickness of infiltration media in CRI system should be 1800mm.