Seeking to enhance the bioenergy of municipal sludge: Effect of alkali pre-treatment and soluble organic matter supplementation

The aim of this research is to enhance the mesophilic anaerobic digestion of municipal sludge from Cadiz-San Fernando (Spain) wastewater treatment plant at 20 days hydraulic retention time (HRT). Two different strategies were tested to improve the process: co-digestion with the addition of soluble organic matter (1% v/v); and alkali sludge pre-treatment (NaOH) prior to co-digestion with glycerine (1% v/v). Methane production (MP) was substantially enhanced (from 0.36 ± 0.09 L CH4 l/d to 0.85 ± 0.16 L CH4 l/d), as was specific methane production (SMP) (from 0.20 ± 0.05 L CH4/g VS to 0.49 ± 0.09 L CH4/g VS) when glycerine was added. The addition of glycerine does not seem to affect sludge stability, the quality of the effluent in terms of pH and organic matter content, i.e. volatile fatty acids (VFA), soluble organic matter and total volatile solid, or process stability (VFA/Alkalinity ratio < 0.4). Alkali pre-treatment prior to co-digestion resulted in a high increase in soluble organic loading rates (more than 20%) and acidification yield (more than 50%). At 20 days HRT, however, it led to overload of the system and total destabilization of the mesophilic anaerobic co-digestion of sewage sludge and glycerine

Correlating Methane Production to Microbiota in Anaerobic Digesters Fed Synthetic Wastewater

A quantitative structure activity relationship (QSAR) between relative abundance values and digester methane production rate was developed. For this, 50 triplicate anaerobic digester sets (150 total digesters) were each seeded with different methanogenic biomass samples obtained from full-scale, engineered methanogenic systems. Although all digesters were operated identically for at least 5 solids retention times (SRTs), their quasi steady-state function varied significantly, with average daily methane production rates ranging from 0.09 ± 0.004 to 1 ± 0.05 L-CH4/LR-day (LR = Liter of reactor volume) (average ± standard deviation). Digester microbial community structure was analyzed using more than 4.1 million partial 16S rRNA gene sequences of Archaea and Bacteria. At the genus level, 1300 operational taxonomic units (OTUs) were observed across all digesters, whereas each digester contained 158 ± 27 OTUs. Digester function did not correlate with typical biomass descriptors such as volatile suspended solids (VSS) concentration, microbial richness, diversity or evenness indices. However, methane production rate did correlate notably with relative abundances of one Archaeal and nine Bacterial OTUs. These relative abundances were used as descriptors to develop a multiple linear regression (MLR) QSAR equation to predict methane production rates solely based on microbial community data. The model explained over 66% of the variance in the experimental data set based on 149 anaerobic digesters with a standard error of 0.12 L-CH4/LR-day. This study provides a framework to relate engineered process function and microbial community composition which can be further expanded to include different feed stocks and digester operating conditions in order to develop a more robust QSAR model

Effect of process parameters on the energy requirement in ultrasonical treatment of waste sludge

Mechanical treatment methods are used as pre-treatment methods in order to enhance the efficiency of conventional sludge treatment processes and the sludge becomes more suitable for its complete treatment. The ultrasound is an alternative method among other methods, but because of its high energy requirement it should be optimized before utilization. This work gives the optimized parameters such as sonication time, sonication power (these parameters are the two factors which play part for energy calculations), type of sludge, cooling requirements and solid content in the sludge solution. Even if the previous researchers prefer to use the energy (specific energy usually), we have found out that both the sonication time and the sonication power have individual importance. For municipal sludge the main conclusion can be summarized as: “high power-short retention time” is more effective than “low power-long retention time”. As this phenomenon may alter from sludge to sludge, various combinations of power and retention time should be tried while keeping the volume small and the concentration below a certain level. The process should be performed at moderate temperatures and the efficiency increases if the sludge is as homogeneous as possible

Thermal Conductivity of Crumb Rubber as Partial Sand Replacement and Recycled Aggregates as Partial Coarse Aggregate Replacement in Concrete

Disposal of waste tire rubber has become a major environmental issue worldwide and is increasing day by day, especially in Malaysia where carbon emission is among the highest in the world. Therefore, recycled waste materials are being used as construction materials in order to create new innovative products that are able to mitigate environmental pollution, reduce the cost of construction and improve the properties of concrete. This study discusses the utilisation of crumb rubber and recycled aggregates in concrete construction and the objective of this study is to determine the thermal conductivity of crumb rubber and compare the optimum strength of concrete materials. 12 cube samples measuring 200 200 100 mm containing different percentages of crumb rubber (0, 1, 2, 3, 4, and 5%) as fine aggregate substitute and 50% of recycled aggregates as coarse aggregate substitute were produced. The concrete grade used for these specimens is grade 35. The curing process was conducted on the samples to achieve the standard strength of concrete in 7 and 28 days. Therefore, the real strength of concrete was measured after the curing process. A slump test was conducted to determine the properties of crumb rubber. In addition, the samples were examined using the guarded hot box method to obtain the optimum percentage of crumb rubber as partial sand replacement in concrete for thermal conductivity. The results show that thermal conductivity (k-value) decreased slightly with the increase in crumb rubber content. However, the quality of concrete also slightly increased as the percentage of crumb rubber content increased. Lastly, based on the results, 5% of crumb rubber and 50% of recycled aggregates were suggested as the optimum percentages to be used in concrete as it achieved the lowest thermal conductivity compared to conventional concrete

Perlaksanaan prinsip lean dalam pendidikan

Kajian ini dijalankan untuk meninjau tahap kepuasan pelajar berdasarkan aspek dalam pendidikan Lean di Fakulti Pendidikan Teknikal dan Vokasional. Menurut pendidikan Lean, terdapat 4 aspek utama iaitu aspek maklumat, aspek aset, aspek proses dan aspek sumber manusia. Data dianalisis menggunakan statistik deskriptif dan inferensi. Dalam menganalisis data secara deskriptif, skor min dipilih untuk mendapatkan ukuran manakala bagi inferensi, ujian ANOVA digunakan bagi mencari perbezaan di antara umur dan juga semester pengajian. Data dikumpulkan menggunakan instrumen soal selidik yang melibatkan sampel kajian yang terdiri daripada 230 orang pelajar-pelajar Sarjana Pendidikan Teknik Dan Vokasional di mana populasinya seramai 290 orang. Data mentah dianalisis menggunakan pakej perisian Statistical Package For Social Science (SPSS). Hasil dari analisis data menunjukkan tahap kepuasan pelajar terhadap keempat-empat aspek pendidikan Lean adalah sederhana. Dapatan juga menunjukkan tidak terdapat perbezaan tahap kepuasan pelajar mengikut umur dan juga semester pengajian secara keseluruhannya. Walau bagaimanapun, dapatan menunjukkan terdapat perbezaan dari aspek aset di antara pelajar semester 2 dengan pelajar semester 3

In-Situ Measurements of Temperature and Emissivity during MSW Combustion using Spectral Analysis and Multispectral Imaging Processing

By using a novel multispectral imaging technology, the 2-D distributions of flame temperature and emissivity were measured in a 16 MW incinerator to co-fire municipal solid waste (MSW) and municipal sludge. A way to establish the relationship between the multispectral flame images and the temperature was proposed by combing the Newton iteration method and Hottel emissivity model. The results showed that the measured temperatures at different locations varied by 31.25% with a fixed steam evaporation rate, and 11.76% with different steam evaporation rates at a given port. The temperatures and emissivities decreased at upper locations due to the lower local soot particle concentration and the change of the measured flame temperatures with load were correlated with the MSW caloric values. Flame temperatures near the left wall were higher than those near the right wall. This deviation was caused by the high moisture content of municipal sludge that inhibited combustion. The emissivities of flame near the right wall were lower than those near the left wall due to the low fixed carbon in municipal sludge. The normalized flame emissivities between the left and the right walls indicated that obvious differences existed in the radiative characteristics of soot, which confirmed the uneven mixing of MSW and municipal sludge. Besides, a spectrometer system was used to measure the release of alkali metal elements including Na, K during the incineration process. The characteristic spectra showed that the alkali metal radiative intensity was related to the moisture content in the wastes. Overall, these results justified that the multi-wavelength thermometry was feasible for monitoring combustion in the MSW incinerator

Ending Subsidized Degradation: The Ocean Dumping Example

There is no way to measure, on a global scale, the pollution dumped directly into the oceans, let alone all the tens of thousands of particulates, toxics, and gaseous substances are added each day to the atmosphere surrounding the New York Bight. The aim of this paper is to develop a user fee framework for the ocean dumping of municipal sludge. Such a proposal requires a radical departure from the standards and enforcement approach of today\u27s legislation. The ocean dumping of municipal sludge, while accounting for only a small percentage of the total waste dumped into the Bight, has proven deleterious environmental and economic consequences

Evaluation of the genotoxic and teratogenic potential of a municipal sludge and sludge-amended soil using the amphibian Xenopus laevis and the tobacco: Nicotiana tabacum L. var. xanthi Dulieu

The toxic, genotoxic and teratogenicpotential of amunicipal sewage sludge was assessed using the micronucleus assay on the larvae of the amphibianXenopuslaevis and with the tobacco somatic mutation test using the yellow–green xanthiDulieu mutant a1+/a1 a2+/a2. The teratogenicpotential was assessed by means of the Frog Embryo Teratogenesis Assay-Xenopus (FETAX). Various doses of the pasty sludge added to a crop soil were tested using the three bioassays. The test systems were performed either directly with sludge or sludge-amendedsoil samples (plant model) or with aqueous extracts (aquatic animal model). Using the tobacco model, we found no mutagenic impact of the soilamended with the sludge, perhaps because the clay-like nature of the soil, with its high adsorption capacity, may have prevented the contaminants from reaching the target. All leachates of amendedsoils produced a significant size reduction in Xenopus embryos. Depending on the soil/sludge ratio, some leachates were found to be genotoxic but were never teratogenic. This battery of in vivo test systems enabled us to estimate the global long-term effects under agricultural conditions with various genetic endpoints on ecologically relevant organisms characteristic of the aquatic and terrestrial compartments