Enhancing low-temperature isothermal convective drying of waste municipal sewage sludge with wood-derived biochar in sequential drying cycles.

In the paper, the results of studies on changes in the concentration of selected polycyclic aromatic hydrocarbons (PAHs) in the reject water coming from aerobic stabilization of sewage sludge process were given. The sewage sludge samples originating from a treatment of municipal wastewater treatment plant and an industrial coking wastewater treatment plant were investigated. A technological study was conducted using a municipal sewage sludge (control sample) and a mixture of municipal and industrial sewage sludge simultaneously. Aerobic stabilization of sewage sludge process was carried out for 21 days. The concentration of PAHs was determined at the beginning of the experiment (day 0) and in seven-day intervals: after 7, 14 and 21 days. The initial concentration of PAHs in the reject water coming from the municipal sewage sludge was over 44 g/dm 3 . Industrial sewage sludge was heavily loaded with polycyclic aromatic hydrocarbons. In a reject water of the mixture of municipal and industrial sludge, the initial content of PAHs reached over 5200 g/dm 3 . During aerobic stabilization of sewage sludge, a decrease in PAHs concentration in reject water was observed. After 21 days of the experiment, the decrease of the sum of analyzed PAHs was in the range of 62-98%.

This paper reviews methods of municipal sewage sludge (MSS) disposal in the Republic of Poland. The MSS amount produced in 2022 in sewage treatment plants is 580.7 thousand tons of total solids. This is related to the increase in the amount of treated sewage and the use of the co-digestion of sewage sludge with waste. MSS generated in municipal sewage treatment plants constitutes waste with code 19 08 05—stabilized MSS. It is subjected to the rules of conduct specified in the Act on Waste. According to data from the Central Statistical Office, in 2022, the most popular disposal method was its use in agriculture (27.1%). Approximately 18% of the MSS from treatment plants was thermally treated. A significant part of MSS is also used for crops, compost production, and reclamation. MSS management requires an individual approach from sewage treatment plant operators and the use of effective disposal methods. Considering the assumption of the circular economy, it is necessary to consider the possibility of recovering valuable raw materials from MSS and producing products for reuse. One of the possibilities of reusing MSS is to generate porous materials. Moreover, MSS can be transformed into multiple types of soil improvers and fertilizers.

Supercritical carbon dioxide drying of municipal sewage sludge – Novel waste-to-energy valorization pathway

The anaerobic co-digestion of fruit and vegetable waste (FVW) and municipal sewage sludge (MSS) is investigated under mesophilic conditions. This was done at a constant hydraulic retention time (HRT) similar to that typically used at waste water treatment plant digesters, 20 days. The effects on digester performance of the FVW:MSS ratio and the organic loading rate (OLR) were examined. Initially the digester was fed with MSS from wastewater treatment plants (WWTP) with an average OLR of 1.03 kgVS(m3 d)−1. The co-digestion of MSS and FVW was performed at various ratios of FVW in the mixture, while increasing the OLRs, from 1.03 to 4.78 kgVS(m3 d)−1. The experimental specific methane production (SMP) was 0.303 m3 (kgVS)−1 for MSS and 0.403 m3 (kgVS)−1 for FVW as single substrate. This value varied for co-digestion with a maximum of 0.445 m3 (kgVS)−1 for a FVW:MSS ratio of 40:60. Alkalinity and pH values remain relatively constant regardless the different FVW:MSS ratios fed. As this ratio increases, the removal of the volatile solids (VS) increased from 38.7% to 82%. The average methane content of digester biogas was about 62–64%.

The construction of new wastewater treatment plants and the modernization of existing ones lead to the expansion of sewage networks, resulting in a sharp increase in the volume of municipal sewage sludge, which translates into a global problem of sludge management. The solution to this problem could be the recovery of energy from sewage sludge in the cement industry to exploit its energy potential. The aim of the present study was to examine the results of laboratory research on the production of alternative fuels based on municipal sewage sludge, plastic waste from end-of-life vehicles, and wood waste (sawdust) from carpentry enterprises. The tests were carried out for waste mixtures designated as PAZO I, PAZO II, PAZO III, and PAZO IV fuels, differing in the percentage of waste used and the type of plastic waste. The following parameters were evaluated in fuels: water content, ash content, sulfur content, and calorific value. Water content of the obtained fuels ranged from 17.1% to 19.4%, the ash content ranged from 2.5% to 3.4%, while PAZO II fuel was characterized by the highest ash content, which was 17.6%, but it remained within the limits permissible for alternative fuels.The sulfur and chlorine contents did not exceed the permissible values for alternative fuels. The calorific value of alternative fuels obtained was high and ranged from 16.5 MJ/kg to 33 MJ/kg. Furthermore, the composition of the individual fuel mixtures was selected to avoid energy-intensive sludge drying, whereas the fuel met the requirements for alternative fuels. The energy properties and water content of the obtained fuels indicate that the maximum amount of sewage sludge should not exceed 25% to maintain the parameters permissible for alternative fuels. Therefore, the analysis of the results leads to the conclusion that the obtained fuels, based on municipal sewage sludge, plastic waste, and wood waste (sawdust), meet the requirements for alternative fuels used in the cement industry. Today, the fuels based on municipal sewage sludge can be more of an alternative to conventional fuels used in the cement industry. The application of the fuels produced in the cement industry eliminates the formation of combustion byproducts in the form of slag and ash since they become a component of clinker. As an additional source of energy, the use of fuels in the cement industry will create an opportunity to move toward the circular economy.

Based on mass and energy balance calculations, this work investigates the possibility of recovering heat and nutrients (nitrogen and phosphorus) from municipal sewage sludge using pyrolysis or combustion in combination with a gas scrubbing technology. Considering a wastewater treatment plant (WWTP) with 65,000 t/a of mechanically dewatered digestate (29% total solids), 550 t/a nitrogen and 500 t/a phosphorus were recovered from the 4900 t/a total nitrogen and 600 t/a total phosphorus that entered the WWTP. Overall, 3600 t/a (73%) of total nitrogen was lost to the air (as N2) and clean water, while 90 t/a (15%) of total phosphorus was lost to clean water released by the WWTP. Both in combustion and in pyrolysis, the nitrogen (3%) released within thermal drying fumes was recovered through condensate stripping and subsequent gas scrubbing, and together with the recovery of nitrogen from WWTP reject water, a total of 3500 t/a of ammonium sulfate fertilizer can be produced. Furthermore, 120 GWh/a of district heat and 9700 t/a of ash with 500 t/a phosphorus were obtained in the combustion scenario and 12,000 t/a of biochar with 500 t/a phosphorus was obtained in the pyrolysis scenario. The addition of a stripper and a scrubber for nitrogen recovery increases the total electricity consumption in both scenarios. According to an approximate cost estimation, combustion and pyrolysis require annual investment costs of 2–4 M EUR/a and 2–3 M EUR/a, respectively, while 3–5 M EUR/a and 3–3.5 M EUR/a will be generated as revenues from the products.

Co-pyrolysis of municipal sewage sludge and microalgae Chlorella Vulgaris: Products’ optimization; thermo-kinetic study, and ANN modeling

ABSTRACTMunicipal sewage sludge (MSS) comes from wastewater treatment plant. Sewage sludge is a waste formed during treatment of wastewater. Wastewater sludge contains a variety of organic and inorganic compounds. The sewage sludge contains mainly lipids, proteins, sugars, detergents, and phenols. Sewage sludge also includes toxic and hazardous organic and inorganic pollutants sources. The MSS contains a significant amount of lipid fraction characterized as oils, greases, fats, and long-chain fatty acid originating from domestic and industrial sludge. The MSS contains a low density of lipids. Activated MSS is a potential source of biodiesel. The MSS is subjected to the pretreatment processes before lipid extraction. The optimum production of biodiesel is faced with huge challenges. The main challenges are collecting the sludge, separating lipids, microbial processing, optimum production of biodiesel and product separation, soap formation, maintaining product quality, bioreactor design, economics of biodiesel production, and regulatory concerns. A major economic factor to consider with respect to the input costs of biodiesel production is the price of the feedstock, which is about 80% of the total operating cost. Other important costs are the labor cost and the price of methanol and catalyst that must be added to the feedstock. The high value of vegetable oils as food products make the production of a cost-effective fuel very challenging.

The physiological and ecological properties of bacterial persisters discovered from municipal sewage sludge and the potential risk

Biochar (BC) is a material that finds many applications in agriculture and environmental activities. The aim of the study was to define the influence of biochar produced from various organic materials: mellow compost (MC), stabilized municipal sewage sludge (MSS), pine sawdust (PS), sycamore sawdust (SS) and oak leaves (OL) on soil enzyme activity, as well as its relations with carbon and nitrogen content. After a 60-day incubation of soil and BC, the activity of dehydrogenases (DEH), catalase (CAT), alkaline (AlP) and acid (AcP) phosphatases was investigated. The basic parameters of soil were also determined: TOC, TN, DOM, pH in H2O, available phosphorus (AP). The highest AP content was obtained in the S + MSS, S + OL and S + MC variants. Enzyme activity was highest in soil with MSS BC, regardless of incubation time. After 60 days, the activity of soil enzymes was inhibited. The obtained results indicate that the response of enzymatic activity to biochar depends on the feedstock material and the incubation time. When using BC as an exogenous matter, it is necessary to determine the TOC/TN ratio. For the very wide range of this parameter, supplemental nitrogen fertilization or mixtures of different biochars should be applied.

Use of MSW compost, dried sewage sludge and other wastes as partial substitutes for peat and soil

This study evaluates the techno-economic feasibility of energy and phosphorus (P) fertilizer (PF) recovery from municipal sewage sludge (MSS) through incineration in new combustion plants. We evaluated the economic impact of five critical process design choices: (1) boiler type, (2) fuel (MSS mono-combustion/co-combustion with wheat straw), (3) production scale (10/100 MW), (4) products (heat, electricity, PF), and (5) ash destination. Aspen Plus modeling provided mass and energy balances of each technology scenario. The economic feasibility was evaluated by calculating the minimum selling price of the products, as well as the MSS gate fees required to reach profitability. The dependency on key boundary conditions (operating time, market prices, policy support) was also evaluated. The results showed a significant dependency on both energy and fertilizer market prices and on financial support in the form of an MSS gate fee. Heat was preferred over combined heat and power (CHP), which was feasible only on the largest scale (100 MW) at maximum annual operating time (8000 h/y). Co-combustion showed lower heat recovery cost (19–30 €/MWh) than mono-combustion (29–66 €/MWh) due to 25–35% lower energy demand and 17–25% higher fuel heating value. Co-combustion also showed promising performance for P recovery, as PF could be recovered without ash post-treatment and sold at a competitive price, and co-combustion could be applicable also in smaller cities. When implementing ash post-treatment, the final cost of ash-based PF was more than four times the price of commercial PF. In conclusion, investment in a new combustion plant for MSS treatment appears conditional to gate fees unless the boundary conditions would change significantly.

Supercritical water pyrolysis of sewage sludge

Following the emergence of the infectious disease COVID-19, caused by the coronavirus SARS-Cov-2, the WHO (World Health Organization) declared a pandemic in March 2020. The pandemic has affected people’s health, social behaviour, and the economy around the world. It has also had an indirect impact on the environment, including atmospheric air quality, related to changes in the levels of pollutant emissions and the amounts of greenhouse gases released into the atmosphere. The observed changes have, in part, been a consequence of restrictions on human movement, which has translated into an increase in water consumption, and consequently into an increase in the volume of wastewater. As a result, a new type of incoming load has appeared in sewage treatment plants. Municipal sewage sludge (MSS) is a waste product from the wastewater treatment process, containing substances that are hazardous to both the environment and humans (bacteria, pathogens, viruses). To dispose of these contaminants, MSS is thermally processed in specially designed installations. Thermal recycling technology is based on a fluidized bed, in which MSS is rapidly transformed at a temperature of at least 750 °C. Organic compounds are oxidized, gasified, and combusted. The exhaust fumes are emitted into the atmosphere. They also carry a load of pollutants, which can affect the air quality both on site and in the surroundings of the treatment plant. This paper presents measurements of air pollutant emissions and pollutant concentrations provided by the Group Sewage Treatment Plant in Łódź Itd. Łódź is a city located in Poland, in central Eastern Europe. The research covers the area of the wastewater treatment plant and its immediate surroundings within a radius of about 1.5 km. The data show the influence of the pandemic restrictions on the concentrations of gaseous substances, bacteria, fungi, and particulate matter on the state of air quality. Increased emissions of NOx (by 86%), PM10 (by 50%), HCl (by 37%), and SO2 (by 16%) were observed compared to the pre-COVID-19 period.

Energy recovery and secondary pollutant emission from the combustion of co-pelletized fuel from municipal sewage sludge and wood sawdust