Press Dewatering of Sludge with Applications of an Electric Field

In the paper industry today, there is a rising concern over the question of what to do with the paper mill sludge. Although in the past most of the sludge was sent to a landfill, this disposal method is becoming less and less acceptable due to increasing environmental concerns, decreasing landfill space and increasing costs. Since sludge contains a large fraction of water, one of the alternatives is to increase the dewaterability of the sludge through the use of electrokinetic forces. Increased dewatering of the sludge would allow for more economical alternatives to sludge disposal, such as incineration, as well as decrease the sludge handling, transportation, and disposal costs by reducing both volume and weight. The main objective of this thesis was to determine if the application of an electric current through a sludge press would increase the amount of dewatering in the sludge. A simulated press that allowed for the sludge to be pressed in-between two charged screens and water to be collected from both the top and bottom of the press was designed and constructed. During experimentation, drainage amounts and final sludge consistency was collected under varying voltage applications and compared to a control run with no voltage. From the results, it could be concluded that the application of an electric field did indeed help increase the dewaterability of the sludge. The results also show that ion migration does take place in the sludge with positively charged particles carrying water molecules towards the negatively charged screen. Further studies in applying this concept at higher pressing consistencies as well as other applications is recommended

Model based study of autothermal thermophilic aerobic digestion (ATAD) processes : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Engineering and Automation of Massey University

An Autothermal Thermophilic Aerobic Digestion process, or ATAD process, is a relatively new sewage sludge treatment process. The ATAD process has been developed for the disinfection and stabilisation of sewage sludge, which is a by-product of wastewater treatment. The end product can be applied to the land as a soil additive or fertiliser with no restrictions, as the process dramatically reduces public health and environmental risks. The process is comparable to the composting process used for municipal solid waste and garden wastes. The process requires oxygen, usually in the form of air, to be applied to the sludge by an aeration system. The oxygen stimulates an exothermic biochemical reaction, which in turn heats the sludge up to thermophilic temperatures (between 50 and 65°C). At these temperatures the pathogenic bacteria, viruses and parasites in the sludge that are harmful to human health are effectively destroyed. The biochemical reaction also degrades a large portion of the organic sludge, which means that unstable, volatile odour generating substances are removed; this reduces the likelihood of smells and the attraction of flies and rodents (vector attraction) to the sludge.[FROM INTRODUCTION

Electrokinetic Treatment of Sludge

Disposal of sludge has become a major issue in the pulp and paper industry because of the decreased space in landfills and the possibility of pollution from the sludge. By increasing the amount of solids in the sludge (dewatering), the sludge could be disposed of using less land or by incineration, composting, or other method. The dewatered sludge is easier to handle also because of its decreased volume. The method of dewatering which was used for the experiment was by electrokinetics. Electrokinetics is the technology of separating solids and liquids from suspensions of finely divided solids or colloidal particles using an electrical potential. Using four different power levels, a final solids level of 5.9% was reached and a decreased volume of almost 50%. This data showed that electrokinetics does have the potential to greatly reduce the volume of material which needs to be disposed of. It may also be able to increase the solids level to a higher level with further modification

Sludge and Ordeals

Is there an argument for behaviorally informed deregulation? In 2015, the United States government imposed 9.78 billion hours of paperwork burdens on the American people. Many of these hours are best categorized as “sludge,” understood as friction, reducing access to important licenses, programs, and benefits. Because of the sheer costs of sludge, rational people are effectively denied life-changing goods and services. The problem is compounded by the existence of behavioral biases, including inertia, present bias, and unrealistic optimism. A serious deregulatory effort should be undertaken to reduce sludge through automatic enrollment, greatly simplified forms, and reminders. At the same time, sludge can promote legitimate goals. First, it can protect program integrity, which means that policymakers might have to make difficult tradeoffs between (1) granting benefits to people who are not entitled to them and (2) denying benefits to people who are entitled to them. Second, it can overcome impulsivity, recklessness, and self-control problems. Third, it can prevent intrusions on privacy. Fourth, it can serve as a rationing device, ensuring that benefits go to people who most need them. Fifth, it can help public officials to acquire valuable information, which they can use for important purposes. In most cases, however, these defenses of sludge turn out to be far more attractive in principle than in practice. For sludge, a form of cost-benefit analysis is essential, and it will often demonstrate the need for a neglected form of deregulation: sludge reduction. For both public and private institutions, “Sludge Audits” should become routine, and they should provide a foundation for behaviorally informed deregulation. Various suggestions are offered for new action by the Office of Information and Regulatory Affairs, which oversees the Paperwork Reduction Act; for courts; and for Congress

Long-term fate of sewage-sludge derived cadmium in arable soils

The focus of this work was to improve knowledge of the long-term fate of cadmium supplied to arable soils by sewage sludge. Emphasis was placed on measured and modelled changes in the solubility and mobility of cadmium, resulting from long-term turnover of both sludge-derived and inherent organic matter of the soil. Measurements were conducted in a long-term sludge supplied field experiment, situated at Ultuna (60°N, 17°E), started in 1956. Furthermore, batch studies on soil samples and modelling exercises in WHAM were performed in order to study the speciation of cadmium in the soil-solution system. A comprehensive model -the SLAM model- was developed to increase the understanding of the influence of soil and sludge adsorption characteristics on cadmium solubility and bioavailability, and the migration rate of cadmium in soil profiles. The long-term sludge supplies had increased the solubility of cadmium, measured in crop cadmium concentration, as an effect of enhanced acidification and increased Cd concentration in the soil. A low Cd migration was measured, attributed to non-equilibrium Cd concentration in percolating water, a high cadmium sorption capacity in the subsoil and root driven Cd circulation in the soil profile. No increased Cd sorption capacity was measured in the sludge supplied soil, despite the almost doubled soil organic matter content. This might be partly attributed to the higher iron oxide and hydroxide concentration measured in the sludge, forming more stable complexes with soil humic compounds compared to cadmium complexes with soil humic compounds. A Monte-Carlo analysis of the SLAM model suggested that the major parameters affecting leaching and crop uptake of cadmium were the cadmium loading and the partitioning coefficient for sludge-derived inorganic material and parameters controlling the effect of pH on sorption. Long-term scenario simulations in SLAM identified critical factors influencing plant cadmium uptake: the cadmium concentration in the sludge, the adsorption capacity of the sludge in relation to the adsorption capacity of native soil and the proportion of the sludge adsorption capacity contributed by the inorganic fraction

Volatile fatty acids production from fermentation of secondary sewage sludge : a thesis presented in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering

Sludge fermentation is used worldwide as an economical means to produce volatile fatty acids (VFA), which can be used as readily available carbon in biological nutrient removal (BNR) systems. In this research, secondary sludge was tested for its potential to generate VFA. Fermentation of secondary sludge was carried out in a lab-scale sequencing batch reactor (SBR). The SBR was fed with secondary sludge of 1% total solids and run with hydraulic retention time (HRT) of 48 hours and 28 hours in phase 1 (40 days) and phase 2 (12 days) respectively. The SBR produced net VFA (expressed as acetic acid) of 365 ±62.5 mg VFA HAC /I which was equivalent to a VFA yield of 0.28 ±0.05 mg VFA HAC /mg VSS feed during phase 1. A change in operating HRT from 48 hours to 28 hours led to a reduction in solids retention time (SRT) from 2.65 days to 2 days in phase 2. The reduction in SRT during phase 2 led to poor hydrolysis and hence could not support the fermentation. Net VFA generation decreased during phase 2 and reached 0 mg/I. Acetic acid was the main acid produced comprising 45% of total VFA content during the run with 48 hours HRT. The effect of total solids (TS) concentration on secondary sludge fermentation was tested using batch experiments. The batch with 2.8% TS secondary sludge showed a maximum net VFA production of 60 mg VFA HAC /I, which appeared to be superior to the 1% TS secondary sludge batch fermentation where no net VFA production observed throughout the test period. Primary sludge (3% TS) exhibited 1200 mg VFA HAC /I in a batch fermentation, which was superior to the net VFA produced during secondary sludge (2.8% TS) batch fermentation. The effects of sonication on fermentability of primary and secondary sludges were tested. A sonic power application of 0.0017 Watt/ml/min density increased soluble content of primary and secondary sludges. In batch fermentations, sonicated secondary sludge improved fermentation over unsonicated secondary sludge. A maximum net VFA production of 130 mg VFA HAC /I was observed in the secondary sludge batch fermentation. In this research work, an investigation into inhibiting VFA degradation in secondary sludge batch fermentations was also carried out. The effects of a methanogenic bacteria inhibitor (bromoethane sulfonic acid) and low pH (range of 4.02-6.07) were considered. The addition of 1 mM bromoethane sulfonic acid (BES) in secondary sludge (1% TS) batch fermentation successfully inhibited VFA degradation. pH values as low as 4.02 showed an inhibitory effect on secondary sludge (1% TS) batch fermentation which led to poor hydrolysis and hence no net VFA generated during the test period. However, low pH values reduced the VFA degradation rate in the batch fermentations. Secondary sludge used in the present research showed the potential to generate VFA. The amount of VFA produced in the present work showed the potential to improve the performance of a BNR system. Moreover, in batch fermentations, VFA generation was improved using various pre-treatments like sonication and BES addition

Diagnosis of an anaerobic pond treating temperate domestic wastewater: An alternative sludge strategy for small works

An anaerobic pond (AP) for treatment of temperate domestic wastewater has been studied as a small works sludge management strategy to challenge existing practice which comprises solids separation followed by open sludge storage, for up to 90 days. During the study, effluent temperature ranged between 0.1 °C and 21.1 °C. Soluble COD production was noted in the AP at effluent temperatures typically greater than 10 °C and was coincident with an increase in effluent volatile fatty acids (VFA) concentration, which is indicative of anaerobic degradation. Analysis from ports sited along the AP's length, demonstrated VFA to be primarily formed nearest the inlet where most solids deposition initially incurred, and confirmed the anaerobic reduction of sludge within this chamber. Importantly, the sludge accumulation rate was 0.06 m3 capita−1 y−1 which is in the range of APs operated at higher temperatures and suggests a de-sludge interval of 2.3–3.8 years, up to 10 times longer than current practice for small works. Coincident with the solids deposition profile, biogas production was predominantly noted in the initial AP section, though biogas production increased further along the AP's length following start-up. A statistically significant increase in mean biogas production of greater than an order of magnitude was measured between winters (t(n=19) = 5.52, P < 0.001) demonstrating continued acclimation. The maximum methane yield recorded was 2630 mgCH4 PE−1 d−1, approximately fifty times greater than estimated from sludge storage (57 mgCH4 PE−1 d−1). Anaerobic ponds at small works can therefore enable sludge reduction and longer sludge holding times than present thus offsetting tanker demand whilst reducing fugitive methane emissions currently associated with sludge storage, and based on the enhanced yield noted, could provide a viable opportunity for local energy generation

Reducing Decomposition Time in Landfills by an Aerobic Process

This experiment was performed to determine if sludge produced by the paper industry could be composted faster by promoting the aerobic degradation process. To perform this experiment, I chose a sludge produced by a virgin pulp mill. Once I collected sludge, it was dewatered to a moisture content of sixty-five percent or less. As soon as the sludge was dewatered, I set up four separate composting systems, three of which were run under aerobic conditions and one that was run under anaerobic conditions. The anaerobic conditions only had sludge and plastic for its bulking agent. In the aerobic systems there were three different types of bulking agents used; pine bark, plastic and compost. In the aerobic systems air was introduced into the system. To determine how fast each of the processes was composting, I collected the gases that were produced by each of the systems. The gases that are produced by an anaerobic process was carbon dioxide and methane, whereas an aerobic process produces carbon dioxide and water. Therefore, by analyzing the gases produced by each of the systems periodically and determining the amount of carbon dioxide produced by each of the systems, one can determine the rate of decomposition of the sludge for each of the separate systems. Also the chemical oxygen demand (COD) was determined for each of the system, before and after the degradation occurred. COD was used to measure that content of organic matter in the sludge. This also helped in determining the degradation that has occurred in each of the systems

Sludge Production and Disposal for Small Cold Climate Bio-Treatment Plants

Ultimate disposal of wastewater sludge has long been a problem which to a large degree has been ignored. Haney (1971) stated that: "Until process sludge can be handled with minimum environmental impact, we cannot claim to have a viable wastewater treatment process". The relationship of sludge disposal to total treatment processes is emphasized by the fact that sludge handling and disposal represents up to 50 percent of the total treatment capital and operating costs (Burd, 1968). Processing of wastewater sludge will, no doubt, receive increased attention in the future because of environmental concerns for our air, land and water. The present technology for processing wastewater treatment plant sludge is well established and includes conditioning, dewatering, and disposal. Many of these processes are highly sophisticated and relatively expensive. Most of the more advanced processes are unsuitable for small wastewater treatment facilities in Alaska.The work upon which this report is based was supported in part by funds (Proj. A-033-ALAS) provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Act of 1964, as amended

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