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The purpose of this study is to understand the relationship between the precursor layer deposited by CuGa-NaF sputtering target and selenidization process. The addition of Na was carried out by using the CuGa-NaF sputtering target. In the CuGa-NaF precursor film, the presence of Na-Ga-F compound was observed. The desorption of fluoride gas from the Na-Ga-F compound occurred, and it accompanied the migration of Ga element. The desorption of fluoride gas enhanced the reactivity with the Se gas in the selenization process. On the other hand, the presence of Na and the migration of Ga impeded the interdiffusion of In and Ga. The decomposition temperature of H2Se gas and the temperature of formation of CIGS were important for uniformity of composition in selenization process. By optimizing the CuGa-NaF film thickness and the multilayer film structure, a CIGS film with a graded composition of In/Ga and the uniformly incorporation Na was obtained.

The influence of free chlorine on the nitrite accumulation in Biological Aerated Filter (BAF) was investigated by adding chlorine in the bioreactor in order to carry out a shortcut nitrification-denitrification. The relationship of the adding dosage and feeding modes of free chlorine and the nitrite accumulation in BAF were also considered. The results show that the nitrite accumulation could be achieved by adding chlorine. When the influent concentration of chlorine was 4mg/L, the concentration of effluent nitrite nitrogen was increased remarkably after the system had been operated for 20 days, and the nitrite accumulation rate could be kept in 60%–70%. The steady state of nitrite accumulation could be maintained with decreasing in the concentration of the influent chlorine, and could also be maintained at a certain degree with the adding mode of intermittent chlorination.

Influence of the pH value of influent on the nitrite accumulation was investigated in a biological aerated filter (BAF) operated in normal conditions. The removal efficiency of ammonia nitrogen and the performance of nitrite accumulation in the BAF were also discussed. The results showed that the ammonia nitrogen removal in BAF was heavily influenced by the influent pH value. Drastically fluctuating of the influent pH value was not conducive to the removal of ammonia nitrogen but beneficial to the nitrogen accumulation. It was found that the continuous rising of pH value could hinder the activity of ammonia oxidizing bacteria to adapt alkaline environment, and there were approximately 77.2% and 88% of ammonia nitrogen were removed in the middle and the upper part of filter bed respectively. It was considered that the nitrite accumulation could be induced in BAF by simply adjusting the influent pH value, but the situation of a long-term and stable formation of nitrite accumulation would get out of hand, at the same time, the removal efficiency of ammonia nitrogen would not high and unstable.

The performance of phosphate removal using hydrothermal modified granular steel slag was evaluated. The effects of steel slag dosage, reaction time, solution pH and initial phosphate concentration of synthesized wastewater on phosphate removal were also investigated. The results show that the modified steel slag is more efficient than raw granular steel slag in phosphate removal. The residual phosphate concentration decreased from 10 mg/L to less than 0.5mg/L at the conditions of solution pH 5-11 and at initial phosphate concentrations of 5-15 mg/L ,when 2g modified steel slag was added into 100mL phosphate solution. X-ray diffraction (XRD) pattern showed that the main hydration products after hydrothermal treatment were calcium hydroxide (Ca(OH)2) and amorphous calcium silicate hydrates (C-S-Hs). Scanning electron micrograph (SEM), energy dispersive X-ray spectroscopy (EDS) and XRD analyses revealed that the precipitates produced in phosphate removal by modified steel slag were the mixture of amorphous calcium phosphate (ACP) and hydroxyapatite (HAP), with the Ca/P molar ratio of 1.58. The results suggest that the modified steel slag may be an effective material for phosphate removal and a potential crystal seed for phosphate recovery.

Study was made on stability and influencing factors of nitrite accumulation in Biological Aerated Filter (BAF)treating simulated municipal wastewater. The possibility of shortcut nitrification–denitrification in low ammonia wastewater treatment was discussed. The mode of natural start-up was favorable to the nitrite accumulation in BAF and the highest nitrite accumulation rate was over 80%. By adjusting pH, nitrite accumulation can take place in BAF. When the influent pH value was 6.5 to 7, the highest nitrite accumulation rate was 57%. But long-term stable nitrite accumulation cannot be obtained only through changing influent pH value. The lower concentration of DO was of advantage to the formation of the nitrite accumulation. When the concentration of DO was controlled to less than 0.5 mg/L, the nitrite accumulation rate can improved significantly to the maximum over 80%. The increasing of hydraulic loading can contribute to nitrite accumulation. When the hydraulic loading was enhanced to 10 m3/(m2•h), the average nitrite accumulation rate can be increased by 52.5 times. The increasing of influent ammonia loading cannot improve nitrite accumulation notably. When influent pH was 6.5 to 7, concentration of DO was 1.0 to1.5 and the filtration rate was 5 m/h, the nitrite accumulation of BAF reactor was of good stability. During 60 days' running, the nitrite accumulation can keep at 65% to 75% stably and obvious shortcut nitrification-denitrification was found.

A comparative study on phosphate removal between activated steel slag and blast furnace slag was investigated. The efficiency of different slags before and after activated for phosphate removal were also evaluated. The results show that the slags activated by hydrothermal treatment are more efficient than raw slags in phosphate removal. The activated slags could be reused for several times and the phosphate removal efficiency could be guaranteed by increasing there action time towards to different reused times. Compared with activated pulverized slags, the activated granular slags could be reused for a longer time for a given initial phosphate concentration. The results suggest that the activated granular slags may be effective materials for phosphate removal. The phosphate removal by activated slag was mainly through chemical precipitation.

The backwashing optimization, which included gas washing, water washing and water rinsing, was carried out in three biological aerated filters with zeolite, ceramic particle and carbonate media. The recovery of headloss and treatment efficiency in the biofilters after backwashing were also investigated for deeper understanding of the relationship of headloss and backwashing in BAF. The results showed that the COD and SS increased in effluent just after backwashing but could be recovered in 2 hours. The concentration of ammonia nitrogen in effluent almost did not change and recovered quickly. All of three BAFs have a promising backwashing performance and operational stability after backwashing. The backwashing procedure of upfollow BAF is suggested as follow: Firstly, air washing 2–3min with air flow rate of 10 L m−2 s−1, then air and water washing 3–5min with both air and water flow rate of 10 L m−2 s−1, and finally water rinsed for 9–11min with water flow rate of 10 L m−2 s−1.