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Wastewater Engineering Treatment And Resource Recovery

Comparative studies on the effects of sewage sludge ash and fly ash on cement hydration and properties of cement mortars

Recovery of phosphorus from incinerated sewage sludge ash by combined two-step extraction and selective precipitation

Croatia produced 21,366 tonnes of dry matter (DM) sewage sludge (SS) in 2016, a quantity expected to surpass 100,000 tonnes DM by 2024. Annual production rates for future wastewater treatment plants (WWTP) in Croatia are estimated at 5.8–7.3 Nm3/people equivalent (PE) for biogas and 20–25 kgDM/PE of sewage sludge. Biogas can be converted into 12–16 kWhel/PE of electricity and 19–24 kWhth/PE of heat, which is sufficient for 30–40% of electrical and 80–100% of thermal autonomy. The WWTP autonomy can be increased using energy recovery from sewage sludge incineration by 60% for electricity and 100% of thermal energy (10–13 kWhel/PE and 30–38 kWhth/PE). However, energy for sewage sludge drying exceeds energy recovery, unless solar drying is performed. The annual solar drying potential is estimated between 450–750 kgDM/m2 of solar drying surface. The lower heating value of dried sewage sludge is 2–3 kWh/kgDM and this energy can be used for assisting sludge drying or for energy generation and supply to WWTPs. Sewage sludge can be considered a renewable energy source and its incineration generates substantially lower greenhouse gases emissions than energy generation from fossil fuels. For the same amount of energy, sewage sludge emits 58% fewer emissions than natural gas and 80% less than hard coal and fuel oil. Moreover, this paper analysed the feasibility of sludge disposal practices by analysing three scenarios (landfilling, co-incineration, and mono-incineration). The analysis revealed that the most cost-effective sewage sludge disposal method is landfilling for 60% and co-incineration for 40% of the observed WWTPs in Croatia. The lowest CO2 emissions are obtained with landfilling and mono-incineration in 53% and 38% of the cases, respectively.

Energy Recovery from Sewage Sludge: The Case Study of Croatia

https://spiral.imperial.ac.uk/bitstream/10044/1/76432/2/JCLP_Yifan%20accepted%20version%20111019.pdf

Recycling incinerated sewage sludge ash (ISSA) as a cementitious binder by lime activation

The potential for using sewage sludge ash (SSA) in cement mortars and concrete is reviewed. The chemical and physical properties and pozzolanic activity of a range of different incinerated SSA samples indicates the potential to exploit the pozzolanic properties of this waste as a supplementary cementitious material (SCM). Using SSA as a SCM increases the water demand and reduces the workability, compressive strength and density of concrete mixes, although these adverse effects may be controlled by modifying the mix design. This represents a beneficial reuse application for a waste that is typically landfilled. However the use of SSA in cementitious materials must be carefully controlled because SSA varies significantly, depending on sludge production method and combustion conditions. Testing will therefore always be required to assess how a specific SSA behaves when incorporated in cementitious materials.

Use of sewage sludge ash in cementitious materials

The potential for using sewage sludge ash (SSA) as a supplementary cementitious material (SCM) has been investigated. Controlled combustion of sewage sludge collected in Croatia from two wastewater treatment plants produced SSA with different characteristics. These were used to substitute for cement in mortar samples. The chemical composition and physical properties of SSA depend on wastewater composition, the sludge treatment process and the combustion temperature. These factors influence the suitability of SSA to be used as a SCM. For three different combustion temperatures (800, 900 and 1000 °C), it was concluded that properties of fresh mortar were not affected while in the hardened state, the most favorable combustion temperature is 900 °C regarding mechanical properties. Regardless of combustion temperature, for all types of SSA used in mortars as cement replacement (up to 30%), the average decrease in both compressive and flexural strength values was less than 8% for every 10% of added SSA. The results presented indicate that using up to 20% replacement of cement by SSA produces mortars that meet the specific technical requirements analyzed in this work.

Influence of combustion temperature on the performance of sewage sludge ash as a supplementary cementitious material

As part of a wider feasibility study on the possible reuse potential of Croatian sewage sludge ash, ash has been produced by laboratory incineration of sewage sludge from two Croatian wastewater treatment plants The Croatian sewage sludge ash was tested for soluble heavy metals according to EN 12457 and results considered in the context of EU landfill Waste Acceptance Criteria With sewage sludge ash alone, the main soluble elements/ions of concern were (in decreasing order): Mo, SO 4 , Cr and Cl When obtained ash was incorporated into cement mortars at cement replacement rates of 20%, EN 12457 leaching of the crushed mortars demonstrated compliance with the strictest limits for inert landfill Waste Acceptance Criteria and well within other limits specified for use in road bases However, much of the reduction in leaching levels can be attributed to the dilution effect of sand used in mortars In the cases of Se, Cr, F and Cl, results imply that the cement used in the mortars actually represents a more significant source of soluble Se, Cr, F and Cl than the produced ash Regardless, the overall results reveal that leaching of heavy metals and other ions is not a significant concern that would prevent the potential reuse of Croatian sewage sludge ash in cement mortars or concretes should Croatian wastewater treatment plants opt for sewage sludge incineration as an alternative sludge disposal and management option

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Environmental impact of sewage sludge ash assessed through leaching

U radu je opisana problematika vezana uz generiranje i zbrinjavanje mulja s UPOV-a (uređaja za prociscavanje otpadnih voda) u Hrvatskoj. Poseban osvrt je dan na mogucnost i opravdanost koristenja pepela dobivenog spaljivanjem mulja. Naglasak je stavljen na ugradnju pepela u betonskoj industriji, pri proizvodnji cementnog morta i betona. U radu su opisani rezultati do sada provedenih istraživanja u okviru svjetske prakse, s primarnim osvrtom na utjecaj ugradnje pepela na karakteristike cementnog morta i betona.

/pdf/use-of-sludge-generated-at-wwtp-in-the-production-of-cement-5cej7nrcwx.pdf

Domagoj Nakić

Papers

Use of sewage sludge ash in cementitious materials

Influence of combustion temperature on the performance of sewage sludge ash as a supplementary cementitious material

Environmental impact of sewage sludge ash assessed through leaching

Use of sludge generated at WWTP in the production of cement mortar and concrete

Effect of lime addition during sewage sludge treatment on characteristics of resulting SSA when it is used in cementitious materials