Characterization of Pretreatment Impacts on Properties of Waste Activated Sludge and Digestibility

Technologies for pretreatment of waste activated sludges (WAS) prior to digestion are of increasing interest to wastewater treatment utilities because of their promise for improving sludge digestibility and reducing the mass of biosolids remaining after digestion. While there has been considerable study of pretreatment processes, a common approach to describing the impact of pretreatments on sludge biodegradability has not been developed. The overall objective of this study was to develop protocols that can be employed to characterize the impact of pretreatment processes on WAS digestion. Sonication and ozonation were employed as models of physical and chemical pretreatment technologies respectively. A range of physical, chemical and biological responses were evaluated to assess the impact of pretreatment on WAS properties as well as digestibility. WAS samples that were generated over a range of solids residence times (SRTs) under controlled operating conditions were employed to facilitate an assessment of the interaction between pretreatment and WAS properties on digestibility. The VS, COD and soluble TKN responses indicated that a significant fraction of the WAS solids were solublized by sonication and ozonation, however, it appeared that the types of materials which were solublized was affected by the SRT at which the WAS was generated and the level of pretreatment. The results indicated that the impact of pretreatment on biodegradability of WAS was not described by solublization values exclusively without considering the SRT of the sludge and the level and type of pretreatment. A higher level of proteinaceous materials was preferentially solublized as the result of pretreatment. Respirometry revealed that both sonication and ozonation substantially reduced the viable heterotrophs in the sludge and modestly increased the readily biodegradable fraction of COD. The ultimate yields of CH4 and NH4 in BMP tests and VFAs in BAP tests revealed that pretreatment marginally increased the ultimate digestibility of the sludges. Only a high dose of ozonation substantially increased the digestibility of the 15 day SRT sludge. However, both sonication and ozonation substantially increased the rate of hydrolysis which is typically the rate limiting process in WAS digestion. The BMP test was not a useful test to evaluate the rate of methane generation due to inhibition of methanogens in the early days of BMP test for pretreated sludges. The comparison between VFA and ammonia responses in day 10 of BAP test and ultimate values of these responses after 60 days in BMP test revealed linear relationships between these responses. According to these relationships, a set of models were introduced in this study. The models can be employed to predict the ultimate methane and ammonia generation using soluble COD, VFA or ammonia responses in day 10 of BAP tests. The BAP test was determined to be a shorter test (10 days) than the BMP (55 to 60 days) test and could provide information on the rates of hydrolysis and acidification/ammonification processes. Characterization of biodegradable and non-biodegradable material in WAS samples was conducted using a simplified ADM1 model. The characterization also revealed that proteins are a substantial fraction of biodegradable materials. The estimated ammonia, VFA and methane values from the stoichiometric model were similar to the corresponding values from the experiments. This supported the validity of the simplified model for all sludges employed in this study

Statewide assessment of air quality changes in Florida during the COVID-19 pandemic

The COVID-19 pandemic has forced many countries from all over the world to adopt extreme measures to suppress the spread of the pandemic. These measures have triggered changes in air quality. Many studies showed an overall short-term improvement in air quality. This study investigates the long and short-term impacts of COVID-19 pandemic on air quality in the State of Florida. Three air quality indicators (AQI) from 69 stations located in 30 counties in the State of Florida were analyzed for 2015–2021. These pollutants are Fine Particulate Matters (PM2.5), Nitrogen Dioxide (NO2), and Sulfur Dioxide (SO2). The long-term changes in pollutant levels were assessed via Time-Lag linear regression analysis (TLR). The results show that PM2.5 levels dropped from 8.88 to 8.24 μg/m3 between 2015 and 2021. However, the ANCOVA test shows that the TLR's slope for PM2.5 is insignificant, with a p-value of 0.859. Thus, there was no statistical evidence that the changes in 2020 and 2021 differ from previous years. NO2 levels fluctuated over the study period between 13.0 and 16.0 ppm with no identified trend. Nonetheless, the regression slope was also insignificant, with a significance of 0.401. The average SO2 concentrations steadily dropped from 4.3 ppb in 2015 to 2.0 ppb in 2020 and 2.62 ppb in 2021, with a regression slope significance of 0.001. It is concluded that pollutants' levels behave differently during the lockdown and release periods, indicating that the lockdown contribution to reduce industrial activities is reflected on air quality rather than mobile source emissions

Sustainability assessment and physical characterization of pervious concrete pavement made with GGBS

The increasing use of pervious concrete as sustainable and environment-friendly paving materials is primarily owed to its ability to reduce pavement runoff. The mechanical and transport properties of pervious concrete with 50% ground-granulated blast furnace slag (GGBS) replacement are examined in this paper. Open-graded 10 mm and 20 mm aggregates were used to attain porosity of 10%, 15%, and 20%. Polypropylene short cut fibers were added to the mix. The clogging potential of pervious concrete exposed to dust was also investigated. The results indicated that increasing the porosity led to a decrease in compressive and tensile strength. Similar findings were reported when smaller aggregates were used. The fiber addition was only effective in low-porosity concrete. Permeability, characterized by its coefficient k, was proportional to porosity and inversely proportional to aggregate size. After 40-year simulated dust exposure, the concrete permeability could be restored with water flushing maintenance process. In comparison to ordinary Portland cement (OPC) concrete, pervious concrete incorporating GGBS is a more sustainable paving solution, offering a reduction in heat island effect and electricity consumption while also alleviating carbon emissions

Statewide assessment of air quality changes in Florida during the COVID-19 pandemic

The COVID-19 pandemic has forced many countries from all over the world to adopt extreme measures to suppress the spread of the pandemic. These measures have triggered changes in air quality. Many studies showed an overall short-term improvement in air quality. This study investigates the long and short-term impacts of COVID-19 pandemic on air quality in the State of Florida. Three air quality indicators (AQI) from 69 stations located in 30 counties in the State of Florida were analyzed for 2015–2021. These pollutants are Fine Particulate Matters (PM2.5), Nitrogen Dioxide (NO2), and Sulfur Dioxide (SO2). The long-term changes in pollutant levels were assessed via Time-Lag linear regression analysis (TLR). The results show that PM2.5 levels dropped from 8.88 to 8.24 μg/m3 between 2015 and 2021. However, the ANCOVA test shows that the TLR's slope for PM2.5 is insignificant, with a p-value of 0.859. Thus, there was no statistical evidence that the changes in 2020 and 2021 differ from previous years. NO2 levels fluctuated over the study period between 13.0 and 16.0 ppm with no identified trend. Nonetheless, the regression slope was also insignificant, with a significance of 0.401. The average SO2 concentrations steadily dropped from 4.3 ppb in 2015 to 2.0 ppb in 2020 and 2.62 ppb in 2021, with a regression slope significance of 0.001. It is concluded that pollutants' levels behave differently during the lockdown and release periods, indicating that the lockdown contribution to reduce industrial activities is reflected on air quality rather than mobile source emissions

Synergic effect of recycled aggregates, waste glass, and slag on the properties of pervious concrete

The properties of pervious concrete made with coarse recycled concrete aggregates (RCA), recycled fine glass (RFG), and ground granulated blast furnace slag (GGBS) were examined. Pervious concrete was produced by substituting coarse aggregates with 0–40% RCA, fine aggregates with 0–100% RFG, and cement with 50% GGBS. Results revealed that incorporating RCA and RFG decreased slump and density but increased porosity and permeability. RCA replacement had a more noticeable negative effect on compressive strength, while RFG replacement was more impactful on splitting tensile and flexural strengths. Abrasion resistance decreased upon RCA inclusion and slightly increased with RFG incorporation. The performance of pervious concrete enhanced with GGBS addition. Its clogging potential was evaluated over a 30-year simulated lifespan. Permeability could be restored to half the original level. While RCA led to lower restoration rates, RFG and GGBS inclusions improved it. Analytical models were developed to correlate and predict the properties of pervious concrete

Application of waste tire rubber aggregate in porous concrete

This study aimed to categorize pervious rubberized concrete into fresh and hardened concrete analyzing its durability, permeability and strength. During the globalization of modern life, growing population and industry rate have signified a sustainable approach to all aspects of modern life. In recent years, pervious concrete (porous concrete) has significantly substituted for pavements due to its mechanical and environmental properties. On the other hand, scrap rubber tire has been also contributed with several disposal challenges. Considering the huge amount of annually tire wastes tossing out, the conditions become worse. Pervious concrete (PC) gap has graded surface assisted with storm water management, recharging groundwater sources and alleviate water run-offs. The results have shown that the use of waste tires as aggregate built into pervious concrete has tremendously reduced the scrap tire wastes enhancing environmental compliance

Application of polymer, silica-fume and crushed rubber in the production of Pervious concrete

Achieving a pervious concrete (PC) with appropriate physical and mechanical properties used in pavement have been strongly investigated through the use of different materials specifically from the global waste materials of the populated areas. Discarded tires and the rubber tire particles have been currently manufactured as the recycled waste materials. In the current study, the combination of polymer, silica fume and rubber aggregates from rubber tire particles have been used to obtain an optimized PC resulting that the PC with silica fume, polymer and rubber aggregate replacement to mineral aggregate has greater compressive and flexural strength. The related flexural and compressive strength of the produced PC has been increased 31% and 18% compared to the mineral PC concrete, also, the impact resistance has been progressed 8% compared to the mineral aggregate PC and the permeability with Open Graded Fraction Course standard (OGFC). While the manufactured PC has significantly reduced the elasticity modulus of usual pervious concrete, the impact resistance has been remarkably improved